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.
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:
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:
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.