Two batteries needed; one out. The other drained?

The title pretty much says it all; the context I present is this: I have a cordless mouse that takes two AA batteries to function. If, for some unfathomable reason, I took ONE battery out (to save on battery life), will the remaining battery still be drawn on, or no?

Not a life-changing question, I know, just curious.

I would say no, the other battery shouldn’t drain. And I know where you are coming from, that other battery is hard to get in and out. i always have new batteries with me for that mouse!

If your batteries are connected in series, which is usually the case, and you remove one of them, the other will NOT be drained, because it will no longer be part of a complete circuit, thus no longer powering your mouse.

OTOH, if your batteries are connected in parallel, then removing one will drain the remaining battery very quickly and may damage the mouse, which is looking for not only a specific voltage, but sufficient current as well. And one battery may not be able to supply it.

I would bet strongly that the first case is the reality here.

So “in series” means one is, say positive up, the other positive down? In that case, yes, my mouse is set up that way (Logitech cordless mouse, something like MX700 or something like that)


The battery orientation may not necessarily tell you anything. My cordless Logitech is powered by batteries in parallel. It runs perfectly fine with just one battery, although I haven’t tried it with only one for more than a few minutes at a time.

My wireless mouse (a Microsoft-branded product) comes alive with only one battery, as well.

Can I hijack this thread? When I was a kid, my Walkman took 3 AAs. The third one always ran down the fastest. Why?

Oh, and it certainly didn’t run with less than the full complement of batteries. You could swap them around and get a little more time, though.

It is possible that the series string was tapped between two cells for a lower “bias” voltage. Possibly to retain (radio station presets) memory or some such.

It is also possible that this cell was positioned near a high power component (or the heat sink for such) and therefore operated at higher temperature than the other cells.

I run my cordless Logitech on one AA battery all the time. I figured “Hey, it works fine with just one; why should I drain TWO batteries?” Maybe I’m doing a Bad Thing.

Oh, and the identical-model mouse my wife uses on her computer needs both AA batteries, or the cursor moves erratically and jerkily. Weird.

Just wanted to add one thought on battery orientation -

If the orientation of side by side batteries is the same it may be a guess as to parallel or series, but I can’t think of any design reason to orientate batteries in opposite directions for a parallel circuit.