Mon 12 Jan 2009
Battery inequality
Posted by David under geek, pass alongs
1 Comment
My family latched on to these battery testers a few years ago, clever little things that gauge the size of your battery and use that to figure out how much power to expect from them, so that they can compare that to how much power they are putting out, thus giving you a reading on how much “juice” is left in them. Lots of batteries seem to have the same kind of thing built into them these days. Whatever.
I’ve been noticing something recently: lots of products use multiple batteries (2, 4, whatever). When the device starts to complain about its batteries being low, I take them out and test them. Often – usually, I’d say – I find that only one of them is actually low. Take out four batteries, three of them test perfectly fine, and the fourth is totally dead. I have to suspect that this isn’t just because the one battery is failing, I think it’s something to do with the physics of batteries. But, I don’t know what. And, I could just be wrong. But, anyone else experience this?
Whatever the case, you might think about checking all of your batteries instead of just throwing them all away when the device they are in says they are low. Curious to hear if others experience this as well.
My understanding of Battery physics is that what happens is as a battery discharges its internal resistance increases. As the internal resistance increases the power available to power the device goes down because some of the power is being lost as heat. This is why you want to replace all of the batteries at the same time because even though only one “tests bad” it tests bad because it was the weak link and the other batteries provided power to heat it up. The remaining batteries all have increased internal resistance too, just not enough that the tester says they are bad, so now the new battery has to heat up all of them as well as provide power to the device. The new battery will not last as long doing this. Of course application might make a difference, if you had battery heated socks, it probably doesn’t matter much (for example).