"Rotating" Batteries - why does it work?

So you’ve got an electronic gadget. A remote control makes a great example. Whatever it is takes two or more cells. As the old AAs reach the end of their useful life, the remote eventually gets to the point where it won’t work anymore.

But it is possible to stretch the useful life of the batteries by switching them around. One they’ve been rotated, they act like they’ve been given a little boost.


I don’t know, but I’ll add the effect is most noticeable to me in portable tape or CD players. My Walkman used to get at least another hour when I was a teenager from switching the batteries. Sometimes it works in remote controls too, but not with the reliability you got with the Walkman.

My guess, and it’s only a guess, is that the connection has become a little bit worn in that spot, and it doesn’t have quite as good contact as it did when new. When you rotate the battery, the contacts in the device contact the battery at a slightly different place. As a final resort to get the last little bit of juice out of a battery, I’ve rubbed batteries vigorously before to heat them up. This will sometimes let your remote run another twenty minutes or so before you have to go out and buy a battery

I’ve found that some devices which use more than one battery will sometimes not drain each battery equally. My wireless mouse here is an example of that; it seems to favor the bottom battery so when I use a battery tester on the two batteries in it after the mouse stops working, one will be about halfway done, and the other will be nearly dead. I can switch them, and they’ll work for a little while.
Might be due to the way the device itself works, or it might just be age and dirty contacts or something like that.

Great site for stuff like this:

I remember reading something about this a long time ago. If everything were perfect, switching the batteries around would do nothing, but in real life products of the reaction that causes the charge to flow will sit at the poles of the batteries and basically clog them up. I’m not 100% sure which battery this would happen to, but I would assume the “bottom” battery. Despite our convention, current actually flows from the negative pole of the “bottom” battery, around the circuit, finally ending up in the positive pole of the “top” battery. Does that make sense to anyone but me?

This configuration:
-[bottom]+ <==> -[top]+

So I can see how the (-) of the bottom and the (+) of the top would get saturated with the by-products of the chemical reaction that generate the current, and your mp3 player goes dead. Basically, the batteries aren’t working idealy - when the “top” battery gets an electron at the (+) pole, it doesn’t always release an electron from the (-) pole. Therefore, the (+) pole of the “bottom” battery doesn’t receive as many electrons from the “top” batttery, so the (+) pole of the “bottom” battery is at about the same state.

So, when you switch them, you’re taking all that bagage away. The “bottom” (+) pole has a lot more potential to recieve electrons, and the (-) “top” pole has a lot more potential to spurt out electrons.

I’m pulling this from vaguely remembered high-school physics, so if there are battery experts out there who remember differently, please edumacate me.

This is not a bad guess, and may be true for some cases. An easy way to test is to take the batteries out, rub the contacts some to get rid of whatever gunk is on them, and then put them back in the same order. If they work better, great. If you have to switch them, it’s something inside the batteries themselves.

Every chemical reaction is benefited by heat - helps chemical bonds break and form - and batteries are just a chemical reaction in a little plasticky metal case. Or, you could just throw the battery at the channel button on the TV. But then you only get to change channels twice… :smiley:

“Current” is a very well defined thing and current flows from positive to negative. You’re thinking about which way electrons flow, which is from negative to positive.

After reading the page, I think you’ve mostly got it, though you’re complicating it by thinking about which battery will be fake dead. It isn’t necessarily the case that either battery will be more likely to go into fake dead mode simply due to position; it’s just that after a while of the battery being used, the inert stuff will be near the electrodes since that’s where the circuit is going to be pulling electrons from. Letting the battery ‘rest’ as it were lets the stuff inside the battery mix around and become evenly distributed again, letting the battery do its thing again.

You are absolutely right - I shouldn’t have used the term “current”. I was talking about the flow of electrons. It always annoyed me a little bit that “current” was the opposite of what’s actually going on.

I still have a sneaking suspicion that the terminals that are actually connected to the circuit will have more inert stuff than the terminals that are just touching the other battery. I have nothing to base this on, other than that I think the (-) of the “bottom” (in my example) will be doing most of the pushing, the (+) of the “top” will be doing most of the receiving, and that friction and other constraints will keep the other parts of each battery from doing their fair share. Switching the batteries will put the respectively clogged up poles of each battery next to each other, and the poles that were doing less work before will be put into action.

That’s not to say that you end up with 2 fresh batteries. Most of the chemical reaction will happen as designed. You just get to benefit from the small amount of inefficiency that occurs in any real-world device.

No. The current is exactly the same at every point in the circuit regardless of the “health” of the batteries.

Actual current is made up of electrons, and flows out of the battery’s negative electrode, around the circuit, and into the battery’s positive electrode. Actual current is only used by component designers. Circuit designers use the standard current convention, which is the opposite (current flows out of the battery’s positive electrode, around the circuit, and into the battery’s negative electrode.).

To answer the OP… I don’t know. The only thing I can think of is that removing and reinstalling the batteries wipes the electrical contacts, and thus reduces contact resistance.

Crafter_Man, thanks, and I always value your input on my dumb electrical questions.

But I don’t think it’s the simple reinsertion/contact scrubbing thing. It doesn’t work of you just take them out and put them back in. That much I’ve been able to verify with past experience.

So there is something to changing the order. And it still eludes me.

aerodave: From a theoretical standpoint there’s no reason why switching the order of two cells in series will make any difference. But there may be 2[sup]nd[/sup] and 3[sup]rd[/sup]-order thermal effects going on. For example, one cell may have higher internal resistance, and thus run hotter. When you switch the cells, the hot battery suddenly finds itself in a cooler environment, and its performance temporarily improves. Or perhaps a voltage regulator or power transistor (which usually run a little warm) is located near one of the cells. Or if the cells are vertically stacked, the bottom cell is heating the top one via convection currents, etc. etc. All kinds of thermal scenarios could be imagined…

Technically, current is just the movement of charge with time, be it any negative charge (in the case of the electrons you speak of) or any positive charge. However, you are correct in the sense that conventional current (positive to negative) was decided long ago when the physics at the atomic level were not known. It just happens that in metals, and hence most circuits, the current is the movement of negative charge.

Interestingly, in various applications the current is actually the flow of positive charge. For example, your household smoke detector works on the current of alpha particles (postively charged) in a gap through the air. When bits of smoke enter the gap, the alpha particles collide with the smoke particles and the current is reduced, setting off the alarm.

Current due to drift of positive charges is very rare. In the vast majority of cases, electrical current is due to movement of electrons. (Even “hole current” is due to electron current.)

I have absolutely zero scientific expertise, but I am a user of remote controls :wink:

For whatever reason, one of them (a TV remote) periodically stops working until I open the battery cover and don’t even take the batteries out and reorder them, but merely spin them around in place. This has been going on now for about 2 years, and it works for several days between spins. Yes, I guess I could put new batteries in, but when it works, it works well (if that makes any sense).

Surely I can’t be the only one with this weirdness. I hope :wink: