Calvin Chu loves nothing more than dissecting mobile computer batteries whether theoretically or actually. Join him as he explains battery technologies and shows you why they sometimes fail. Boom!

Very interesting article. I always suspected that intense heat is what causes batteries to have shorter lifespans and even explode, but never understood why. Now I do.

However, the article seems like it was published before it was finished. Hear me out, what I intend with this is constructive criticism, not destructive--I have no reason to say bad things about THG, the author, etc., I only wish to improve the site or at least give my two cents as to what I want to read. First of all, page 7 seems more like the middle of the article than the end--it leaves you hanging. While the "conclusion" should wrap things up, we have no clear solutions or scenarios in which we could make any conclusions.

Also, I would love to know some info about NiMH vs. LI-ion as far as how many notebooks use one versus the other. I am guessing that typically the "desktop replacement" notebooks use mostly the Li-ion batteries for the higher Wh, while the NiMH batteries are used in the "slim-line" notebooks for extended battery life--am I correct?

Lastly, why are the sony batteries being recalled? What specifically? Why do some work and others blow up? I just felt like we didn't have enough of that to truly make any sort of conclusion.

Thanks again for the article and I definately learned alot, but I wish I had just a touch of insight as to what is causing the sony batteries to explode.

When batteries are in series you add the voltage and mAh stay the same. When batteries are in parallel you add the mAh and voltage stays the same.

On page 6 at the bottom you mention the current 1.2V@2700mAh packs would equal 9.6V at 10800mAh. That is not possible with 8 of these batteries. They are either hooked up in series providing 9.6V@2700, series-parallel combo for 4.8V@5400mAh, 2.4V@10800mAh or parallel for 1.2V@21600mAh. To get 8 1.2V batteries to 9.6V@3000mAh would require 8 1.2V@3000mAh bateries. The original batteries are probably more of a custom C or sub-C size battery since you would have space to spare swapping in 8 AA batteries and C size batteries were around 3000mAh back then. My guess would by the original square packs were 8 C batteries rated for 1.2V@3000mAh hooked up in series to achieve 9.6V@3000mAh. Which current C NiMH are rated around 4500-5500mAh and higher. Which would almost double the capacity.

I quick way to check the math is total voltage times total mAh is the same as individual voltage*mAh*number of cells.
1.2V*2700mAh*8 cells=25920mW Hours
9.6V*2700mAh=25920 mW Hours
9.6V*10800mAh=103680mAh

I have never opened up a laptop battery so it is interseting that some use regular battery sizes in a series-parallel combination. This makes for cheap upgrades.

In reply to the response

Size for size and weight for weight LI-ion provides more power. Whether you want more power(desktop replacement) or longer life(Slim-line) Li-ion is your best choice. The determining factor over what is used is price. NiMH is cheaper than Li-ion batteries.

Size for size and weight for weight LI-ion provides more power. Whether you want more power(desktop replacement) or longer life(Slim-line) Li-ion is your best choice. The determining factor over what is used is price. NiMH is cheaper than Li-ion batteries.

I prefer a cheaper battery with longer run time and capability of functioning longer than just 12-18 months personally...that is what I meant by "battery life"--battery life is the time before it will no longer charge or work, and run time is how long it runs on a full charge.

I own a desktop replacement laptop 17" widescreen and i use it as a portable computer. Like most desktop replacement computers it is on a desk and plugged in 99% of the time. NiMH would actually be a better cheaper alternative since it has a longer battery life. Battery run-time is more important to slim-line notebooks where smaller and lighter is better. They spend alot of time unplugged for mobility so I would expect to see Li-ion in slim line due to lower weight and longer runtimes. Almost all laptops these days come with Li-ion. Even the cheaper $6-700 laptops now have Li-ion. The manufacturer could care less about battery life(only 1 year warranties) and focuses on run-time hence the switch to Li-ion. Its more impresive to sell a laptop with 8 hour run-time than a laptop with a battery that will last several years.

Cheaper and longer run-time dont go together.

Thanks for your input so far. As of this date and time the author is investigating the possibility of a few errors in the article. We'll post fixes as soon as we have them.

Well, I do radio control car racing, and the r/c hobbyists know for a long time that you should never ever charge your batteries unattended. Several r/c helicopters or cars have gone up in flames. I'm surprised that the computer industry didn't know about this problem until a major catastrophe happened to the laptops.

There is a new company out there called a123systems.com, and it claimed that its lithium batteries are safe and environmental friendly. Also it can charge very fast. This battery has been used in commercial drills, and other power tools that now can power 36 or 48 V. Previously, the voltages for power tools were only 24v.

the company is still young and needs funding to mass produce its safe batteries. check out at: http://www.a123systems.com/html/home.html

Author here.

I'm afraid you caught me in a case of some bad napkin calculations, so kudos to Pomaikai for the good catch. I'll be sending up maybe a couple of extra photos to show the series and parallel network inside the battery in more detail. So Pomaikai, I owe you a beer, and I owe myself a dope slap for spending more time photoshopping the darned water tower diagram than rechecking my napkin math. I've gone ahead and fixed the math.

Thanks!
Calvin

Hi Bourgeoisdude,

My goal for the article is mostly to go over very lightly the basic concepts and technical terms (like V, and mAh, etc) and to crack open the black box (literally) and see what ticks underneath with one cocked at the exploding battery phenonenon. It's really by no means an deep explanation or technical analysis. It's an article in the vein of "What goes on beneath that manhole cover?" and while you can imagine all kinds of alligators and victorian pipeworks, it helps to shine a flashlight down there, snap some pictures and not so much discuss city blueprints as report what is seen and heard.

There were some parts that I've seen and experienced that I didn't go over. But if you want to hear more, just let me know.

As for NiMH vs. Li-ion--most new production laptops have moved to the Li-Ion packs. Most notebooks are designed to maximize battery life. And with the cost of designing custom battery packs being what they are (high!), the initial incremental cost of deploying Lithium-ion vs. NiMH is the same. Unless the battery pack is a standard mass produced part, NiMH gets cheaper more dramatically during mass production. So the manufacturer's rationale is often to deploy with a Lithium-Ion battery pack, and if you only ever sell a few thousand of that model laptop, a NiMH custom battery would not have been cheaper, and in the worst case, the battery life would have been pretty good. And furthermore, whoever got fired for choosing Sony?

Specifically, Sony admitted to metallic contamination of the Lithium-ion chemicals. If a metallic impurity (such as random particles of metal) gets inside the battery cell, chances are, nothing happens. The probability that these random particles randomly locate themselves into the formation similar to a wire, or a configuration that allows a short circuit to occur inside the cell is astronomically small. In fact, it might only ever occur to 5 in a million, or something small like that. That looks a lot like 0% probability if you round it up. But that was what happened. Somehow, random cells would short themselves out and do a runaway meltdown.

Basically, if you connect the + and the - side of a Lithium-ion cell, you better be far away, and fast. Luckily, the protective circuitry in between the + and the - prevents that from occuring. In the case of the Sony recall, it became possible for the + and - of an individual cell to *internally* get stuck together, and then, there is nothing in between to stop that reaction from getting away.

Thanks,
Calvin

Nearly all off the shelf rechargables are NiMH for reasons of safety, but, increasingly, NiMH is becoming pretty darn competitive with Li-ion.

My inspiron 1200 notebook and its identical Inspiron 2200 brother were the last Dell to be offered with a NiMH battery. Interestingly enough, a Li-ion battery was an available upgrade. Now here's the kicker: the NiMH battery was 9.6v, while the Li-ion battery is 14.8 volts. To the best of my knowledge, the mobo is the same, reguardless of battery used. The AC adapters were also the same: 60 watt 19volt max output. Is that a head-scratcher of what? I'm currently using a regular NiMH battery, but the Li-ion type offers extended battery runs (it is a 65watt/hr vs the NiMH's 43watt/hr).

A few more corrections to article, the initial chart comparing NiMH to Li-Ion:

- NiMH are not "usually" rated to only 300 cycles

- NiMH are not "usually" limited to capacity/10 charge rate. Most can be quick charged at C/1 now, but a few lower like C/5. If it can be discharged in (suppose 2 hours in a laptop) it can also be charged in same amount of time. This doesn't mean it won't reduce lifespan some, but with a smart charger the rate should drop prior to Delta-V switching to trickle mode as the last ~ dozen % of charge is the highest heat generation rate.

- Safety Circuit in NiMH also has the "Pressure Relief Gas Vent" as listed on Li-Ion as an integral part of every cell- it need not be listed on a pack spec, is true per cell.

I don't mean to suggest these make NiMH equivalent or better than Li-Ion, as there's always the lower energy density.

I've picked up a Lacrosse NiMH charger--this is the one that allows you to adjust the charging rate. It is a smart charger. One thing I found about NiMH is that if you charge them fast, they get hot. If they get hot, they are to some degree outgassing internally and once the gas escapes (e.g., was not catalyzed) then you begin to lose life on the battery. You can try this experiment with a Lacrosse -- put one pair of AA NiMH and charge at a very high rate, and put one pair of AA NiMH and charge at a very low rate. And repeat, you'll find that the *capacity* diminishes on the NiMH that is fast charged. It is safe to do so, but it means the rating is no longer the same. Hope that makes sense.

Some very cool chargers get around this issue by putting a fan to cool down the battery during fast charging. This could work, but not all chargers have fans.

Calvin

To Joe Friday:

I'll help you solve your head scratcher. Your laptop has a built-in protection circuit that regulates the voltage. Here's why. When a battery is used, the voltage begins to drop. Internally, the laptop electronics require voltages like 3.3V, 12V, 5V, and so on. Since a battery by its nature has a different voltage depending on how much "Juice" is left -- the regulator circuit is responsible for converting this voltage to the correct voltage. It turns out that if you pop in a battery with a different voltage, but within the tolerance of the circuit, you are OK, because that is the regulator doing its job. In fact, I've plugged a Thinkpad 19V adapter into another laptop that needed 14V and it was just fine. If your laptop has a good enough regulator, it just works.

Calvin

It's a fancy charger, but not as "smart" as I meant. The ideal fast charger starts at a high rate, drops to a lower rate by itself before reaching Delta-V, and then at Delta-V, drops down to an elevated trickle, perhaps around C/7 for 30 minutes to an hour then finally a C/15-20 trickle if not turning off entirely. Naturally the charger would have a thermal shutoff too, but should never be using it.

That is either not worded very well or is incorrect. A typical moderate to fast charger will cause the batteries to get fairly warm ("hot" is a rather subjective term since it's actually a degree rise over ambient as well as interpretation), but there is no outgassing at this point. You can recharge NiMH in a typical 4 hour charger (which is roughly C/3.5 rate) and expect no outgassing.

It is already known that to charge at a very fast rate, you'll still need a top-off trickle for a period of time to reach maximum capacity. This has nothing to do with overheating then outgassing.

If charging a cell too fast, yes that could help but we aren't usually trying to charge THAT fast, and as mentioned previously one of the keys in keeping heat down is how smart the charger is, if it reduces voltage prior to delta-V there is a lower rate of heat generation.

There is no need for a fan with decent quality (lower impedance) batteries in a C/3.5 or longer charge cycle, unless the ambient temp is rather high which could certainly be the case if the batteries were in a running laptop, but never is it necessary to charge as slow as C/10 for *reasonable* life. If the only concern is the longest life possible, it is true a rate as low as C/10 may help slightly, but it is practically never the case that a device charges at C/10 default rate for this reason, rather it's to keep the charger cheap, using only continual trickle current or a timer shutoff without the need for a microcontroller.

Nice, basic and comprehensible !


So just a wild question,
would it be possible to rebuild a battery that went bad (by for instance replacing cells with modern cells) - say for my very old Compaq Armada 1110?