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May 23, 2022

Dr. Mark's Power Supply and Battery Web Log (Blog) Archive 1

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Table of Contents

How effective is desulfation in restoring lead acid batteries?
2800 Amp Hour Portable Battery Pack
Pictures of mistreated lithium-ion battery
New Web Page: VA versus Watts
What is the shelf life of an SLA.

New Product: 12 to 8.5 volt DC/DC converter

Can I get shocked from the output of a wall-mount power supply?

What is the difference between a 3.6 volt and a 3.7 volt lithium-ion or lithium-polymer cell?

Comment on the Altair Nanotechnologies press release of 10 Feb 2005?

More comments on ultra-fast charge batteries

New ultra-large lithium ion cells and batteries.

Q: What discharge voltage marks the optimum time to begin charging an SLA battery?

Q: I am having a hard time finding 24 volt lead acid or sealed lead acid batteries.

Q: Mark, why is this 9 volt adapter putting out 17 volts?

Batteries for Power Wheel Toys

New Spot Welders

Can you charge a 12 volt sealed lead acid battery with a 6 volt charger?

Recharging the unrechargeable: Lithium

How much lithium is in a lithium-based cell?

New Feature, power supply humor

Q: How much does refrigerating batteries extend their life?

Q: I have a device (printer) that needs 12 volts DC, but I can't run it directly from a car cigarette lighter, how do I regulate it?

Q: What about refrigerating batteries during storage to keep them fresh longer? How about freezing?

Q: I didn't find any information about adding extra battery pack to UPS. If possible, which type of batteries would be the most suitable to connect to the UPS? My UPS uses two 6V, 7AH batteries.

Q: Why does my wall-mount or desk-mount transformer make humming or buzzing sounds now? It only started up recently, and sometimes when I bang it it stops for a while.

Q: When is a lithium-polymer battery not a lithium-polymer battery?

Q: Can a lithium-ion battery be rejuvenated?

Charge a NiMH with a NiCad Charger?

Too many Amps?

What is venting and what causes it?

Tell me about the liquid-liquid rechargeable battery.

What is the longest lived primary battery?

5-10 year life rechargeable batteries?

Charging lithium-ion cells at low temperatures

Why are there no B sized batteries?

What is the polymer in "lithium polymer batteries?"

Stable 12 volts in a car

Lithium thionyl chloride versus lithium ion

Coin cell holders

Self-discharge rate definition

Temperature compensation of lead acid battery charging and gassing

Memory effect in lithium-ion?

Memory effect in lead acid?

Q: How effective is desulfation in restoring lead acid batteries?

We have successfully rejuvenated batteries, both flooded and sealed lead acid, with electronic desulfation. Our multi-bay charger at /Shopcharg.htm uses a simple but effective method of raising the charging voltage when it detects a high AC impedance.

Desulfation is the process of removing the insoluble lead salts from the batteries plates. This gets the battery operating again if that was the only problem. However, it can't repair corroded plates or restore lost water to the battery. Thus none of the rejuvenation methods, either impedance-based, pulsed, or DC, will bring a battery back to new, but they can often bring a battery back to life for more service.

I talked at length to a man whose business is rejuvenating and recycling lead acid batteries. He said that after opening hundreds of batteries, many of the failed sealed lead acid batteries (including valve regulated, absorbed glass mat starved electrolyte, and gel cells) had run out of water for some reason or another, and there is no safe and effective way to get the water back into them.

Huge Portable Battery Pack

This the completion of a project to build a huge portable sealed lead acid battery pack for a customer that wanted to run some low power equipment for a long time while on the road. The total weight is about 3000 pounds (1350 kg). Click here for pictures.
Disintegrated battery pictures

One of our customers has graciously permitted us to post some interesting pictures of what happens to a small lithium-ion battery when your charging circuit goes wild. Take a look by clicking here.
New Web Page: VA versus Watts

We have had so many people call us confused about the difference between VA (or Volt·Amps) and watts that we have created a web page that explains the difference. Click here to view it.

Q: What is the shelf life of an SLA?

I bought a spare SLA1075 12v 7.2 ah battery and don't plan on using it much. It's a spare. If I keep it charged and store it at room temp will it be ok?

A: The long answer to this question is at /Storage.htm , but the short answer is that yes, if you keep it charged (top it off every 3-6 months) it will last for a long time.
Announcement: New Product--12 volt to 8.5 volt DC/DC converter.
We have four products that we have been pressing to get finished. The first is a 12 volt to 8.5 volt converter with 10 amp output. The primary use for this gadget is to power Playstation II™ games in the back seat of a car or van. Do I have to remind you that even in a traffic jam you shouldn't be balancing the game panel on the steering wheel?
Click here for the link.

Some playstations use AC only. These which would require an inverter to run them off a 12 volt system.

Our other products-in-development are a 72 to 12 volt DC/DC converter for use in locomotives, a DC/DC lead acid battery charger for charging 24 volt batteries in cars and vans, and a 48 to 12 volt DC/DC converter . I expect that the charger will be the next one on the shopping cart, hopefully in mid September.
Q: I have lots of wall-wart adapters that come with various appliances. They have a metal connector. If I disconnect the appliance while the wall-wart is still plugged into the wall am I in danger of getting a shock?

A: Generally, in the industry, and according to safety agencies, there is no shock hazard if the output is less than 60 volts. If the power supply that is running your equipment is more than 60 volts there will be a special connector that will not allow you to be shocked by it.
They are also isolated from the mains so there isn't a shock hazard from either of the power supply outputs to ground.

But I don't know of any case where such a high voltage is used in a wall-mount or desktop power supply.
Q: What is the difference between the 3.6 volt and the 3.7 volt lithium-ion and lithium-polymer cells?

A. This question has been on my mind for a few months. There is a lot of folklore out there about this. It confused me for two reasons. Firstly, I have never heard of a higher charge voltage for some cells and not others. Secondly, the 3.6 is just a rule-of-thumb average of the battery voltage anyway . The actual voltage varies between 4.2 volts and 3 (or 2.8) volts during the discharge. It doesn't have one voltage. You can't just put a meter on a cell and say "this one is a 3.6 volt cell" or "this one is a 3.7 volt cell."

So I asked a friend who has a PhD in battery chemistry and has been designing, testing, and manufacturing lithium ion and li-poly cells for over 15 years. Here is his answer:

There is no difference between 3.6V and 3.7V cells. The reasons why people say 3.6V in one case and 3.7V in other cases are due to discharge rate. If you discharge your lithium ion cells with 0.2C rate, the middle point voltage of the cells is 3.7V. If you discharge your lithium ion cells with 2C rate, the middle point voltage of the cells is 3.6V or even lower. The middle point voltage of a lithium ion cells, including Polymer Lithium ion Cells, is between 3.6V and 3.7V, variable upon discharging rate.

In other words, it is mostly marketing hype. Now the modern cells tend to keep their voltage higher during discharge than the old ones, so a marketing person could easily say "this makes the average higher, so let's call it a 3.7 volt cell."

But why stop there? Why not rate the voltage as the peak voltage and get the jump on everybody? "It's a 4.2 volt cell, demand nothing less!"

So don't get caught up with the hype when selecting a battery.
Q: Comment on the Altair Nanotechnolgies press release.

Update: in 2018, 13 years later, there still does not seem to be a product based on Altair's battery technology.
A: Here is part of the press release:
"RENO, NV -- (MARKET WIRE) -- 02/10/2005 -- Altair Nanotechnologies, Inc. (NASDAQ: ALTI) announced today that it has achieved a breakthrough in Lithium Ion battery electrode materials, which will enable a new generation of rechargeable battery to be introduced into the marketplace, as well as create new markets for rechargeable batteries. These new materials allow rechargeable batteries to be manufactured that have three times the power of existing Lithium Ion batteries at the same price and with recharge times measured in a few minutes rather than hours."

<snip> "The nanomaterials Altair is developing are the next generation of electrode materials for lithium-ion batteries and Altair's research and product development is laying the ground work for a new generation of ultra high power lithium ion batteries," commented Dr. K. M. Abraham. "A key requirement to the above applications is the ability to recharge the battery very quickly, for example in a few minutes. Current Li Ion batteries are incapable of such quick charge times because of the chemistry of the anode materials. Altair has found a solution to this with their nano-sized lithium titanium oxide."

A: My comments: It has been long known that the smaller the particle size the faster the charge and discharge you can do. So extrapolating that down to "nano-sized" is easy. But what is also well known is that small particles have a high self-discharge rate, so battery factories that are actually making viable products try like the dickens to eliminate the small particles so their batteries will keep a charge. Extrapolating this to "nano-sized" means that you have a battery that won't hold a charge very long.

I could be wrong, but this looks like stock market hype. Their stock jumped on February 10th, but has settled down again since them.

Disclaimer: Since PowerStream is also developing new cathode materials I might be a little biased on this!

More comments on the practicality of ultra-fast-charge batteries.

I thought I would also weigh in on the practicality of ultra-high-charge-rate batteries. If you have a small, say 1 amp hour, battery and you want to charge it in one minute, how many amps do you need? That is right, math fiends, 60 amps. So the battery can charge quickly, but you need a $300 charger to do it. Of course 2 minutes cuts this down to 30 amps, and 4 minutes cuts this down to 15 amps, etc.

Then you also have to have terminals, wires, connectors that can handle 60 amps and you may have something that looks like a semi towing a Miata, the semi being the cables and the Miata being the battery.

You also have to consider the charging characteristics of the battery. Lithium-ion cells require a constant current-constant voltage algorithm. The amount of current you can dump into the cell is limited by the chemistry's requirement to keep the charging voltage below 4.2 volts. It is conceivable that you could get 80% of the charge into the cell in the first minute, but to get the remaining 20% could take 59 minutes.

Of course there are a few applications that would justify the equipment necessary to charge a battery in 60 seconds. But it isn't laptops or cell phones.
Large Lithium Ion Cells and Packs Update
We have been selling large lithium ion cells and packs for over 4 years now. They have gone mostly to military, military contractors, robot builders, undersea autonomous vehicles, and similar projects where the customer needed to store a lot of energy in a small space and weight, but to whom long life and reliability were secondary factors.

However, I was never happy with those batteries. They didn't like to be discharged quickly, often didn't last very many cycles, and had a tendency to swell up irreversibly because the plastic cases were able to let water vapor diffuse through them into the electrolyte, which then caused gasses to form. Sometimes they would get to the customer's lab dead on arrival. So I tried to discourage most potential customers, hoping that the quality would improve, but in 4 years nothing change significantly. In particular I was not willing to recommend these early cells to engineers that were developing products which would require a reliable battery and a reliable source of supply.

Last March I was visiting a friend who was the general manager of a lithium battery factory in China. I told him that I was selling large cells but I didn't like the quality of the engineering or the manufacturing of these cells and was anxious to develop a better battery for our customers. He explained to me why the cells we were selling were poorly designed. We discussed our needs and he agreed to partner with us to make and sell large cells, starting with 12 AH and 60 AH. By the first of May we had cells ready for sale.

My friend has a PhD in battery chemistry from a university in Europe and has many years experience in battery design and manufacture while working for companies in the USA and China.

I am extremely pleased with the results. What we finally have are big rectangular cells enclosed in hermetically sealed stainless steel cases. Since they were designed and tested by an engineer who is an expert in performance and reliability they can be truly considered to be a big leap forward in the state-of-the-art. They will put out currents of up to 3C reliably, are designed to have a long cycle life (though they are so new we don't have lifetime data as yet), and don't swell up when you charge or discharge them.

We also now have a cell-balancing battery management board which can be produced for managing any number of cells. We can design and produce a new configuration within 3-5 weeks with no minimum order required . The variety of capacities has expanded to include 12AH, 15AH, 18AH, 60AH and 80AH. These can be paralleled to form 24AH, 30AH, 36AH, 120AH, and 160AH packs or more. We have made 120 AH packs for a national laboratory, and have qualified cells and packs in several applications.

We also have chargers designed around a platform that can be easily modified to charge different cell arrays, available in the same time frame with no minimum order.

The more experience I get with these the happier I am. We finally have a series of large li-ion cells that are viable options for commercial products.

Take a look at them at /LLL.htm
Q: If I’m using the BP2.3-12 (or any other general purpose 12v SLA), what discharge voltage marks the optimum time to begin charging the battery pack again?

A: For lead acid batteries--including sealed lead acid (SLA), valve regulated lead acid (VRLA), gel cells, and flooded lead acid batteries. The optimum time to recharge is "now." They like to be fully charged as much as possible, and don't mind being recharged if they were just partially discharged.

However, to prevent damage to the battery don't discharge below about 10 volts for a 12 volt battery.

Q: I am having a hard time finding 24 volt lead acid or sealed lead acid batteries.

A: Systems that require 24 volt lead acid batteries almost always use 6 or 12 volt batteries in series. Making and then handling a battery with 12 cells is too cumbersome. So either use four 6 volt batteries or two 12 volt batteries in series.
Q: Mark, why is this surplus 9 volt adapter I bought putting out 17 volts?

A: An unregulated wall wart will put out an open circuit voltage of much more than 9 volts, 17 volts is definitely possible. These regulate the voltage by using the resistance and impedance of the transformer windings, so the output voltage will vary with the output current drawn.

Just like a hose will squirt farther when you put your thumb over the end to restrict the flow.

A wall transformer that is rated 9 Volts 1 Amp will give a nice 9 volts when you draw one amp, but will give less voltage if you draw two amps and more voltage if you draw half an amp. Regulated power supplies give you the same voltage no matter how much current you are drawing.

Batteries for Power Wheel Toys

Q: I bought a ride-on power wheels toy from Wall-Mart and need new batteries. Can I use motorcycle batteries?

A: There are tons of ride-on toys for kids that use lead acid batteries, Fischer-Price is into this in a big way with all kinds of licensed brands from Harley to Jeep. When the batteries finally die (these are kids, aren’t they?) what do you do to replace them?

First, you need to use a sealed lead acid battery. Many motorcycle batteries are not sealed, so can leak sulfuric acid when tipped over, overcharged, etc. You might think that motorcycle batteries are non-spillable, but this is not the case for most of them. Most motorcycles don’t get tipped over often enough to justify non-spillable.

The non-spillable batteries are sealed lead acid (SLA), gel cells, valve regulated lead acid (VRLA) and absorbed glass-matt (AGM). Use one of these technology, and yes I realize that these categories overlap.

Second, motorcycle batteries are designed as starting batteries, not deep-discharge batteries. This means that you won’t get many charge-discharge cycles if you use them in deep discharge. To start an engine you need high current for a short period of time, and to fit on a motorcycle you need to be as small as possible. So the compromise is to use a lot of surface area, but foil-thin plates. After a few deep discharges the plates corrode through and you are an unhappy Dad.

All general purpose non-spillable batteries are made for deep discharge, except those made for motorcycles. So you might save on the price of the battery, but it won’t last very long, making it a poor economic choice!

Our SLA batteries can be found at /BB.htm . These are the highest quality available and so are a little more expensive than the cheapest batteries, but no matter what you end up paying, make sure that you are getting non-spillable general purpose or deep-discharge sealed lead acid batteries.

Announcement new spot welders:

Our inexpensive capacitive discharge spot welders have been so successful that we have introduced two new models, the 220 joule (220 watt-second) and the 330 joule (330 watt-second) models. The old, 110 joule, model is still plenty powerful enough for welding tabs to batteries, but the new models can be used for thicker gauge applications. They are all the most inexpensive precision spot welders in the world.

Q: Dr. Mark , I was reading your BLOG, and thought you would most definitely be able to answer this question...

Can I use a 6v battery charger to charge a 12v battery? I bought a new battery-powered weed-whacker at a garage sale very cheap because they couldn't find its charger; I thought I had a 12v charger at home, but it turns out to be a 6v charger! Will it work? Thanks for your time and consideration. Nice site! Mike

A: Mike, you need at least 2.15 volts per cell to start the lead-acid chemistry flowing the right way to charge, that is 12.9 volts for a "12 volt" battery. The 6 volt charger isn't going to make it.

Q: I am concerned about the regulations on shipping lithium-containing batteries by air. In particular, I don't have a clue how much lithium is in a, say CR123, battery.

A: The theoretical "electrochemical equivalence" of lithium is 3.86 amp hours per gram. If you check at /b.htm
to find your lithium battery ( lithium thionyl chloride, lithium sulfur dioxide, lithium manganese dioxide, lithium-ion, or lithium polymer ) you can find typical values for the capacity of the battery in Amp-Hours. The CR123 is a lithium-manganese dioxide battery with about 1300 mAH, so it would have 1.3/3.86 = 0.34 grams of metallic lithium per cell.

Q: I came across your website, and I think if anybody can answer a question I have been needing the answer to I think it's you. I have a Surefire M6 flashlight (the most powerful one they make) and it uses a cylinder of six(6) SF123A lithium batteries. The problem is I am always using the Surefire 500 lumen lamp, and the 6 batteries have a useful life of about 20 minutes. Gets expensive. Is there any charger available that can recharge them? Thanks, Bob.

A: Dear Bob,
This is a current topic. The SF123A is just a relabel of the CR123A, a lithium-manganese Dioxide primary cell. Yesterday I got a call from an engineer that tried charging a CR123A. It exploded, put a hole in his work bench, and filled his garage with foul-smelling residue. These batteries use lithium metal as the anode. So to recharge you have to electroplate metallic lithium. This can only be done under very special conditions. My new friend was probably creating dendrites that eventually pierced the separator, causing the explosion.

Announcement: Power humor web page.

Everybody knows how humorous engineers are, and everybody enjoys a joke. We intend to write, collect and feature jokes, anecdotes, short films, and cartoons on this page, all oriented to batteries and power supplies. The first offering is the lyrics to "Who let the Smoke Out." Check it out at /powerhumor.htm

Q: Dear Mark, I too had heard about extending the life of batteries in the fridge. Yet may I ask you to go one step further and offer up how "extended" such actions provide and to what kinds of batteries this would apply to please. I am seeking info generally for the typical household battery. Thank you, Mike in St. Louis

A: The easiest to put numbers to is primary, non-rechargeable cells.

Zinc-carbon cells lose about 14% per year at 25 degrees C, 4% per year at 10 degrees C, and 1.8% per year at zero degrees C.

Alkaline cells lose about 6% per year at 25 degrees C, 2.2% at 10 degrees C, and 1.4% per year at 0 degrees C.

So you can see that if you don't store your cells for years on end, it doesn't make much difference. However, it also means that you don't want to store your cells next to the furnace, in a hot garage or shed, or in your glove compartment during a hot Arizona summer!

Q: I have a device (printer) that needs 12 volts DC, but I can't run it directly from a car cigarette lighter, how do I regulate it?

A: A car's electrical bus, what usually comes out of a cigarette lighter plug, is typically 14 volts while the car is running, 13.5 volts when the car is not running, and can drop below 9 volts when the car is starting.

Sensitive electronic gadgets may not like this variation. To regulate and stabilize the voltage you can use the UDC1212-8 , which is a buck-boost converter that takes in a wide range of voltage and puts out a regulated 12 volts.

If the equipment can handle 14 volts fine, but shuts down or locks up when the car is started, you can use the PST-SR700 , which stays alive while the car is being started, and can keep the equipment powered even if the battery sag due to the starter motor is as low as 6 volts.

Q: What about refrigerating batteries during storage to keep them fresh longer? How about freezing?

A: Recently the discussion floated back to the old question of refrigerating batteries. Most chemical processes approximately double in speed for every 10 degrees C increase in temperature. This includes the chemical processes of battery self-discharge and corrosion. So the warmer a battery is the shorter its storage life.

Refrigerating batteries during storage does increase the life of batteries, but often it isn't worth the hassle.

A cold battery is also going to give lower current output due to the same process, so make sure you have enough time to warm them up!

How cold is too cold? Now it is true that it is bad to freeze batteries because the ice crystals can damage the structure of the battery (the separator for example). But when does a battery freeze? NiCad, NiMH and Alkaline batteries use 30-45% KOH in water solution. The freezing point of this at the eutectic of 31% is -60°C (-76°F). No freezer is going to go that low.

Lithium-ion cells are harder to pin down, but most of their electrolytes go to -40°C, (which is also -40°F). Lead acid batteries depend on the state of charge, a fully charged battery will freeze between -70°C and -30°C. A fully discharged lead acid battery will freeze at about 0°C. So unless it is a discharged lead acid battery, don't worry about storing batteries in the freezer.

Q: I can't find any information about adding an extra battery pack to uninterruptable power supplies (UPS). If possible, which type of batteries would be the most suitable to connect to the UPS? My UPS uses two 6V, 7AH batteries.

A. This is tricky. Often there is only enough heat sinking available to run the UPS inverter for the amount of time that the internal battery would give. So adding external batteries would cause it to overheat. If the backup is designed to use external batteries, then the heat will be able to be dealt with, and the general purpose BP-xxxx batteries will work well. Adding a couple more 7AH batteries will more than double your backup time, since the entire battery assembly will discharge more slowly.

Q: Why does my wall-mount or desk-mount transformer make humming or buzzing sounds now? It only started up recently, and sometimes when I bang it it stops for a while.

A: Most consumer transformers are made with laminated steel cores. This means that there is a stack of metal plates inside the box with two coils wrapped around them, the primary and the secondary. These plates are usually stuck together with wax or varnish at the factory to keep them still. The 60 Hz (60 cycles per second) from the house AC voltage actually causes the steel plates to expand and contract 60 times a second. In cheap transformers this can cause the plates to loosen, and eventually start to flap together. Now 60 Hz is audible. It is a musical note between A# and B, two octaves below middle C. (If the engineers that decided to standardize on 60 Hz were musicians they might have picked 61.74, which is B1, and the world might be a more harmonious place). When this happens you can start to hear a humming or buzzing from the transformer.

Adventurous, handy kind of people have been known to open up the case and apply fingernail polish, epoxy, model airplane glue, etc. to the plates to quiet them down again by sticking them together. However, not very many transformer cases can be easily opened any more, and since I don't want to be sued I don't recommend it!

You might also be interested to know that the wavelength of this 60Hz noise is 220 inches, 5.5 meters, or 18 feet. This means that as the sound bounces around in the room it can create fairly sizeable nodes and antinodes, or places where the waves cancel or reinforce. So you can be laying in bed saying "that transformer hum is driving me crazy," while your wife three feet away can't hear anything so she thinks you ARE crazy.

Q: When is a lithium-polymer battery not a lithium-polymer battery?
A: When it is a lithium-ion battery in a foil package. I just got back from China where I had one of our battery engineers explain the difference. When lithium polymer batteries were first developed they used an ion-conductive plastic sheet for the separator and electrolyte. Since there is no liquid involved another innovation was introduced, that of a foil package. This means that the battery has no metal casing, only an aluminized plastic bag exactly like a package of potato chips. If the package gets torn it is not good for the battery, but at least it doesn't catch on fire, which is what may happen if you pierce the shell of a lithium-ion cell.

Well the problem with lithium-polymer is that the polymer does not conduct ions very well, so the amount of current you can draw is low. To expand the applications the conductive polymer was replaced with a conductive gel. This gave higher current, but still kept the electrolyte in place. This isn't as safe as the true polymer, but still works. At least the corrosive, toxic, flammable electrolyte stays in place if the foil container is compromised.

The next step, of course, is to replace the gel with a liquid electrolyte and separator. In this case the only difference between the liquid-polymer cell and a lithium-ion cell is the foil bag. The advantage is that the currents can be enormous. The disadvantage is that these cells are dangerous. Piercing the thin foil bag releases the flammable, toxic electrolyte, which can catch on fire if any water gets on it. The electrolyte is also corrosive. Not many companies are willing to take a risk like this, but a certain Korean firm made a fortune marketing such cells to the RC airplane market.

The so-called high-current lithium-polymer cells are just a lithium-ion cell in a plastic bag, be careful if you design one of these into your product.

Q: Can a lithium-ion battery be rejuvenated?

A: In general, if you can't get it to take a charge it is dead. However, just because it is at zero volts doesn't mean that you can't try to charge it. It may just mean that the charger does not recognize that it is hooked up. A few short minutes trying to charge the battery with an external power supply (don't go over 4.2 volts per cell) may give it enough "oomph" for the charger to take over.

In laptop batteries sometimes the cells get so far out of balance that the only safe thing to do is to blow a fuse. This is one of the functions of the safety board. These laptop packs typically have 6 or 9 cells in them. In this case if you just open it up and fix the fuse you are getting into dangerous territory, because the original manufacturer put this feature in so you wouldn't be in danger. By fixing it yourself you may cause a fire or explosion. So with laptop batteries, there is no way to rejuvenate the battery.

Q: I have a NiCad (nickel cadmium) battery charger, is it OK to charge NiMH (nickel metal hydride) batteries with it?

A: It depends. Most of the time a slow, overnight, style charger that is designed for NiCads will work fine because the charging method for both chemistries is very close to the same. However, for fast charging (1-5 hours) it might not work well.

For chargers that use the slump in voltage (minus delta V) to detect the end of charge the NiCads give a much stronger signal, which might be missed if you are charging NiMH, and therefore the cells will be overcharged (they will get hot). Minus delta V can be used with NiMH, but the charger must be more sensitive to the drop in voltage at the end of charge.

For chargers that use a timeout the NiMH will not get a full charge, which isn't a bad thing, and since most smart chargers go into a trickle the NiMH's will eventually fill up completely. Remember that NiCads and NiMHs don't mind having a partial charge, in fact in some applications NiMHs are never fully charged in order to give them a longer service life.

For chargers that rely on a change in the temperature curve slope a NiCad fast charger will charge a NiMH battery just fine. For more information see our web pages on charging NiCad and NiMH batteries.

Q: Will a power supply with too many amps hurt my laptop?

A: Fully regulated power supplies, such as laptops use will work well with your laptop as long as there are enough amps. So if your laptop requires 3 amps and you use a 10 amp power supply you are cool. The amperage rating of the power supply tells how much current can be supplied, the laptop determines how much is actually drawn. Similar to having a 400 horsepower engine, you don't know you have all that power until you actually call on it. The voltage should be rated fairly close (but not necessarily exact) but the amps don't matter as long is they are equal to or greater to the specification.

HOWEVER: For unregulated power supplies, i.e. wall transformers or wall warts, the voltage regulation depends on the current drawn, so if you have a 9 volt 1000 mA wall mount transformer you need to replace it with a 9 volt 1000 mA transformer (unregulated) or a 9 volt regulated power supply with 1000 mA or more. The difference is unregulated versus regulated.

Q: What does it mean when a battery or cell "vents?" What causes venting?

A: There are several reasons that a cell or battery can build up gas pressure inside it. Overcharge, very fast discharge, internal shorting, and high temperature are the ones that come to mind. If the pressure was allowed to build up indefinitely the cell would eventual rupture with great force. However, in normal operation it is desirable to retain the gas in the cell because it can be recycled by recombining the hydrogen or oxygen.

To prevent explosions, most cells and batteries have an intentional vent that will let the gas out at a specified pressure, high enough to retain the gas under normal operation, but low enough to keep the case from rupturing. When an alkaline, NiCad or NiMH cell vents some people can hear the high-pitched squeal, I can't. But I can notice a white residue on the tops of the cells. This is dried potassium hydroxide, which is soon converted by atmospheric CO2 to potassium carbonate. Neither of these is poisonous, but the potassium hydroxide is lye, which can eat clothes and cause skin irritation.

After a cell vents it may still retain most of its capacity, it is not necessarily dead.

Q: Have you ever heard of a "new" battery discovery that uses two (2) liquids and after the electron flow is completed, all one has to do is refill the compartments with fresh liquid? The chemicals are non-acidic, was invented by a female French scientist and was introduced on the discovery channel. The feature on Discovery stated that it would be a while before the battery would reach the market, because "service stations would have to be outfitted to handle the ingredients". To date, I have not been able to find anything more about it. Any information you could provide would be appreciated.

A: This is probably the vanadium redox battery. It is described on our battery chemistry page /BatteryFAQ.html#redox . This is by no means a new battery technology, but it is an interesting battery because if the two liquids should be mixed it will not destroy the electrolyte, because they are the same vanadium ions at different valence state. It is one of a class of batteries that are called "mechanically rechargeable," meaning that the recharging is done by changing out components of the battery, not by applying a recharge current. So the service station flushes out the old liquid, recharges it and has it available for another car.

Q: What is the longest lived primary (non-rechargeable) battery?

A: The lithium thionyl chloride battery could qualify for this. Data sheets give 10 year shelf life, but there is no fundamental reason why they couldn't last much longer than this, and if you don't mind losing 50% of the capacity during the storage process and kept them away from heat you could have usable capacity after 30 years of storage.

Q: I need a rechargeable battery that will last 10 years in service. My boss is suggesting lithium-ion. Any suggestions?

A: This is an open question, since you don't say how many charge/discharge cycles you need. Unfortunately lithium ion won't last 10 years. Industry rule of thumb has been "2 years whether you use them or not." The technology has been improving, and some are now saying "3 years whether you use them or not." The reason for the short life is that the electrolyte reacts with the lithium ions and creates crud on the electrodes.

This, of course, depends on your criteria for failure. The 2-3 years is based on 20% permanent loss in capacity. I have a lithium ion battery for my cell phone that is 5 years old, but it is only good for one call a day (which is enough for me). No one will guarantee lithium ion rechargeable cells for 5 years, or even 3 years. Another problem with lithium-ion is it doesn't do well with fast discharge times. The higher the rate of discharge the more reaction occurs with the electrolyte, and the faster the crud builds up. There are lithium polymer batteries that can give higher currents, but lifetime is also a problem with them. NiCad is the best for long life. NiMH may be a possibility, it depends on how many charge/recharge cycles. NiCad is by far the best for fast charge. Lead acid lasts 3-5 years on standby. So the only possibility for a 5-10 year life is NiCad, and then only if you charge them right, don't discharge them past 1 volt per cell, and over-specify them so that you still have enough run time even though they are starting to degrade.

Q: Data sheets for lithium-ion cells say not to charge below zero degrees C, and safety battery management boards usually prevent the cells or packs from charging if they are cold. Is this a lifetime or a safety issue?

A: My friend Evgenij Barsukov answered this question:

"The main reason is this - at low temperature the equilibrium of the reaction Li + C6 -> LiC6 is moving towards left (e.g. metallic Li). As result, you have more of lithium metal deposition rather than intercalating compound. Having Li-metal is bad because it reacts with electrolyte so: 1) you lose your efficiency because you can not recover lithium that has reacted. 2) The product of this reaction is insoluble, so you are losing Li for good, so it is a permanent capacity loss. 3) You generate a film of insoluble stuff which electrically disconnects particles and so increases battery impedance. These are the main reasons not to charge at low temperatures, but there are others - impedance is a lot higher so your voltage (at the same current) will almost immediately jump to 4.2V and current will start to fall. So you will reach the taper termination earlier, or you will terminate by timer and you will never fully charge the battery (more likely to 70-80% at 0C)." Regards, Evgenij

Q: Why are there no "B" sized batteries, there are A, C, and D, but I haven't ever seen a "B."

A: There has been a standardized size for B cells as long as there has been one for the C cell, they are 21.5 mm in diameter and 60 mm long. You can see that they are not very different (20%) from a C cell (26 x 50mm) in volume, but are longer. For some reason, as engineers developed products they rarely used Bs and Cs took over. "A" cells also never took off until recently they have become popular in NiCad and NiMH and later lithium ion packs. There are also specifications for E, F, G and J ( I don't know what happened to the H and I).

Note: Don't get the B sized cylindrical cell confused with the B+ battery used in early tube radios. These were lead-acid batteries that put out the 65 volts necessary for the B+ power supply of the tubes.

Q: What is the polymer in "lithium polymer batteries?"

A: Originally lithium polymer batteries used a conductive polymer as both the separator and the electrolyte. The polymer was polyethylene oxide, which becomes conductive when mixed with lithium salts, later polyvinyl fluoride. As you can imagine, this caused a high internal impedance (the voltage sagged a lot when you tried to pull out even a few hundred milliamps of current). Gradually the polymer was replaced, first with a gel, then a crystallized gel with liquid-filled pores, and lately with a microporous membrane saturated with electrolyte (in other words, no polymer). As far as I know, all these technologies are still available.

The one common factor in all these technologies is that the cells are put in a foil pouch rather than a metal can. So the latest lithium polymer batteries are just lithium-ion batteries in a pouch.

Q: I need a DC to DC converter to provide a regulated 12 volt output when the input is voltage from a car. I will be using this regulated power to run a computer in my car. Also when the power supply is off, will this converter consume any power from the battery?

A: Typically the voltage on a car's electrical system hovers around 13.7-14 volts when the engine is operating, 10 to 13.5 volts when the engine is turned off, and 8-12 volts when the car is starting. In addition, there is noise and there may be spikes and dropouts in the voltage. The DU500 and DU700 are boost converters which regulate the voltage to 13.8 volts, eliminating noise and delivering a steady voltage, which is great for car stereos and other equipment that was designed to run in a car in the first place, but they can't be adjusted to put out 12 volts unless the input is less than 12 volts because they are boost converters.

"Boost converter" means that they can only increase the voltage from the input to the output. If you need 12 volts regulated you need a buck-boost converter which can maintain a steady 12 volts whether the input voltage is above or below the desired output voltage. The PST-DC/1212-8 is a buck-boost with a wide range of input voltages and delivers a stable 12 volts output.

Q: How do the ER Series lithium batteries compare with lithium ion?

A: The ER series lithium thionyl chloride batteries are not rechargeable. They use lithium metal and will explode if you try.

Primary batteries (i.e. non-rechargeable) usually have more capacity than secondary batteries (i.e. rechargeable) Since lithium thionyl (ER), lithium sulfur dioxide, and lithium manganese dioxide (CR) cells do not need to be rechargeable they can have much more capacity per volume and weight than rechargeable lithium ion and lithium polymer cells. These cells all contain lithium in its metallic form, and so are very dangerous to try to recharge. Lithium-ion cells are called lithium-ion because the lithium is always in a chemical compound, never as a metal. This makes the lithium-ion cells much safer.

Q: You sell rechargeable coin cells and coin cell chargers, do you also supply the coin cell holders to go along with them?

A: We don't supply these yet, though it would make sense to do so. I know of three manufacturers that make battery holders, Memory Protection Devices (MPD), Keystone, and Eagle. You might look at the Mouser or Digikey catalog if you have one, or look online.

Q: Hi Mark, Can you explain on the rechargeable prismatic cells what is meant by "self-discharge is less than 10% per month."

A: It means that after the first month 90% is left, after the second 81%, after the third 0.729, etc. In other words 0.9^x where x=number of months. It DOESN'T mean that you are empty after 10 months. After 10 months in this hypothetical case, you would have 0.9^10 = .34, or 34% left.

Q: Dear Mark, I have a lead-acid battery question. I am trying to determine what the temperature compensation should be for the OTC voltages for a fully charged battery at rest. For example if it is 2.11 VPC (volts per cell) at 80 degrees F, what would it be for 100 degrees F? or at 20 degrees F? My sense is that there would be a positive temperature coefficient, The question is how much plus or minus per ten degrees F? .9 mv?

A: The open circuit voltage is
E = 2.047 + RT/F ln (alpha(H2SO4)/alpha(H2O))

Because the natural logarithm can change signs this can be complicated, but since all commercial lead acid batteries run relatively high concentrations of acid, the thermal coefficient is normally positive, and about +2 mV/degree C. However, the gassing voltage has a negative coefficient, which is not very linear and there is a table for it on http://www.powertream.com/sla.htm

Q: Mark, I know that you say that Nickel Cadmium batteries rarely exhibit the memory effect, can you explain this?

A: If you discharge fully once every 100 times you will never notice any memory effect in an application, it takes about 30 partial recharges to the same state to be able to detect it in the lab. Most of what is blamed on the memory effect is either persistent overcharging (leaving a battery on charge for months at a time on a cheap "not-smart" charger) or a worn out battery.

Q: Do Nickel Metal Hydride cells have the memory effect?

A: Manufacturers have been saying for years that they don't. However, actual lab measurements show that they have the same memory effect as NiCads. It is the nickel hydroxide that is the problem, not the cadmium. The reason that manufacturers have gotten away with saying that there is no memory effect is that the effect is rarely seen, even with NiCads. The proof is in Dave VanHorn's web page, here is the smoking gun: http://www.dvanhorn.org/NIMH/Memory-HRAUC-30.pdf
The dotted red curve is the derivative of the output voltage dV/dt, and you can see the sag in the curve between 24 and 48 minutes. This is the voltage sag as the hardened nickel hydroxide is being cleaned off.

Q: What about lead acid, do they suffer memory or "top-off" problems?
A: Don't be confused, different battery chemistries are different! Lead acid doesn't have a memory problem, and it insists on being fully charged at all times for a long life. Lead acid's problem is that it doesn't like to be stored at partial charge, and can suffer permanent damage if it isn't kept at full charge. Nickel metal hydride, nickel cadmium and lithium-ion cells can be stored at any state of charge, but the lithium-ion will last longer if you store them at a partial charge state. See /Storage.htm

Disclaimer: Information presented here is the opinion of the author. No warranties regarding the correctness or value of this information are implied or should be assumed.

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