I made a little custom data logger. It's powered by a rechargeable AA Ni-MH battery.
Typically, it lasts about 2 weeks on one battery. Then it uses a low voltage cutoff to sound a low battery alert, after which I swap in a new rechargeable battery and pop the old one back in the charger.
A few weeks ago, I had a little minor problem where the whole thing got wet. The battery was found to be pretty hot. The data logger was completely destroyed and has since been replaced. After the battery had cooled down, I put it back in the charger (BQ-CC17). It seemed to charge normally, but I can't say for sure since that charger doesn't calculate capacity or anything.
I used the (potentially damaged) battery in the (newly replaced) logger. It worked fine for about a week, then abruptly died (no low battery alert). My speculation is that the voltage dropped off so abruptly that the logger didn't have much or any time between the low voltage cutoff and the battery dying completely. (The logger worked fine after putting in a new battery).
So, my question is this: Is it possible for a battery to "fail" in such a way that it shows the following symptoms:
- Appears to work normally to roughly half its normal capacity
- Voltage drops off almost instantly
If the battery were totally destroyed (internal short circuit), I would not expect it to work at all, certainly not for half the time it normally does. Is there an "intermittent short circuit" failure mode, where e.g. the short circuit occurred based on ambient temperature/humidity/phases of the moon, rather than being related to reduced capacity?
P.S. Please, no answers telling me that getting a new battery is cheap and easy. I already have. I just need to satisfy my academic curiosity.