Will a torch shine with charged and dead batteries in it?

01 November 2009

Question

If I have a torch and I put three batteries in it and two are fully charged and one is fully drained, will the torch still produce light?

Answer

I think that very much depends on the chemistry of your batteries. A battery is essentially a chemical reaction which is split into two halves and the only way - and let's say you got part half A and half B, the whole lot's got to happen to be driven in any way that can happen is quite passing electron through your circuit. And eventually, the battery runs out because you run out of all the chemicals you need for the chemical reaction. Now, basically you're saying, if we apply a large voltage and carry on pushing electrons through the battery, what's going to happen? That would depend on what other the chemical reactions go on to move charge through the electrolyte in the battery. Normally, that's often quite inefficient. If you've got have something like a lead acid battery which is symmetrical, it will just start up in the wrong direction. Certainly a very simple that acid battery will - and so, it will turn into battery but pointing the wrong direction. If you have other chemistries of batteries, it could cause all sorts of havoc and it will depend on the exact chemistry. It will certainly become a very high resistance. It will work for a bit but eventually, it's going to run out of - it will either stop or it could do all sorts of strange things to your battery, it's certainly going to damage a rechargeable battery.

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