Respect Your Batteries

Seriously.  These seemingly innocuous little things can kill you if you mistreat them.  So be kind to your batteries, alright?  Don’t overcharge them, or short them out, or put them into hot ovens, or stab them, or shoot them with rifles, etc, etc.

Just an ordinary SLAB...

You see, I’ve had more than one close call with a battery in my day.  Like the time I was working on a regenerative motor drive circuit and suddenly had a gate driver IC turn into a dead short across 24V of lead-acid batteries.  Have you ever seen a 14-DIP glow red hot?  I have.  The aftermath looks something like this:

A Very-Failed Gate Driver IC

And then there was the time I was trimming some wires on the end of a string of twenty LiPo cells.  Somehow, I managed to temporarily short the two ends of the string with the diagonal cutters I was using.  End result?  The enormous surge of current actually  vaporized a chunk of metal from the tip of the cutters.  Oops.

Of course, misuse isn’t the only cause of battery misbehavior.  Overuse can cause problems as well.  Just yesterday, my UPS shut down and started beeping incessantly.  Now, in its defense, I’ve been using it almost non-stop for the past six years and have never replaced its battery.  In the last year, it’s probably warned me two or three times that it needed a new battery, but until yesterday, I’ve ignored it.  For one thing, I operate it at only about 10% of its full-load rating.  For another, it’s no longer supporting any equipment that needs to remain online during a power failure.  So I figured, eh, I don’t mind if it only lasts a few minutes during an outage – I’ll grab a new battery for it with my next Digi-Key order.

Well, when the unit finally shut down for good yesterday, I figured I’d better go ahead and pull out the battery.  Once I had the cover removed, however, I discovered three causes for concern.  First, the battery was unusually hot (about 130F according to my IR thermometer).  Second, it had swolen so much that I could no longer slide it out of my UPS.  Third, it had split in four places on its bottom, as you can see here:

Battery failure...

Battery failure (closeup) ...Yea, that looks pretty bad, right?  Electrolyte had actually started leaking out of one of the splits and had begun a bit of rusting on the battery housing cover.  You can see a close-up shot of this to the right.  Perhaps even more unnerving, however, is that when rotated, you could hear bits and pieces of something rattling around inside the battery.  That can’t be good.  Batteries aren’t supposed to have things rattling around inside of them…

So presented with this new problem, I grabbed my safety glasses and moved everything into the kitchen.  Why?  Well, I figured that if the thing started smoking or something while I was attempting to remove it from the UPS, I’d just toss the whole works into the oven (which was of course turned off), close the door, and grab the nearby fire extinguisher.  Fortunately, I didn’t need any of that.  After a bit of sweat and a lot of not-so-gentle prying, the battery popped lose and started to slowly cool.

Here’s something I don’t understand though: why did this sealed lead-acid battery split open at the bottom?  Isn’t that what the circular cuts on the top of the battery are designed for?  To vent any pressure accumulating inside the cells?  And yet, if you scroll back up to the top of the page and take a look at the first image shown, it sure doesn’t look like any of those vents have even cracked.  I don’t think I’ll be buying my replacement battery from YUASA though, I can tell you that…

And now, to wrap things up, more examples of why you should be nice to your batteries (especially LiPo cells… these things are psychotic):

 

By the way, Lithium battery chemistry has greatly improved over the years.  The risks of such spectacular fires are now quite low.  But please, don’t push your luck.  Respect.

2 thoughts on “Respect Your Batteries”

  1. Respect mah hustle and mah L to the i to the P to the o.

    Eh, where was I? I once connected a 74hcXX backwards to a 5V supply. In terms of damage it was really boring. Didn’t overcurrent, didn’t get glowing hot. After a couple of minutes, a small chip of plastic was ejected from the side of the case. The only way it could’ve hurt me is if it had hit one of my eyes directly.

    As far as batteries go, my MacBook battery recently started swelling. I took it out, which I don’t mind since the laptop is half-broken and I’m using it as a stationary computer anyway. And I think that was part of the cause for the problem as well, since I’m always running it with the lid closed, so the heat has a hard time escaping. Later I’ve read that a swollen battery actually isn’t necessarily a safety problem, but I didn’t want to take the risk. The only problem now is that the fancy magsafe connector sometimes comes loose if I’m moving the computer.

    As far as your battery is concerned, I’m guessing that there are three individual cells inside the plastic cover and that one or more of them has started leaking and corroding the plastic. I don’t think your issue is necessarily high pressure. Or if it is, the safety cuts might only react to excessively higher pressure, not a slightly elevated pressure for an extended period of time. Another hypothesis is that the battery has gone almost dry so that what you’re hearing is actually chunks of electrolytic residue. However, since this is a lead battery, I think the risk of an explosion is pretty low, unless the battery is shorted or overheated. Lead batteries are much tougher than Li ion ones, which are really ridiculously fragile.

    1. Haha, nice. I’ve had a couple of ICs pop like that as well. In the same gate drive project mentioned above, I accidentally applied 24V (again, lead-acid batteries) to an I/O pin on an AVR, which was configured as an output at the time. It blew a small hole in its case almost instantaneously.

      Good point about the battery cracking due to something other than very high pressure. Could definitely have been a combination of heat and corrosion on the plastic. I believe this 12V battery actually has six cells, but they’re likely arranged in a 3×2 configuration. The cracks must run along the interfaces between each cell. Good thought about the drying as well. I’ll have to do a little more reading on the subject. You know, I probably should have saved the thing and attempted to open it, but I’m sure that wouldn’t have been very safe or environmentally friendly (instead I dropped it off at a Home Depot battery recycling bin).

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