How does a rechargeable battery recharge?

I was talking about batteries in my physics class and it got me thinking, how do rechargeable batteries work?

Rechargeable Batteries

A battery (like the ones that died in my mouse this morning) uses chemical reactions to create a charge. Basically, (in really simple terms) the electrons get pushed up the equivalent of a really big hill by the energy released from a chemical reaction. There are lots of electrons at the top of the hill (the anode) and they don’t want to be so close together. Remember like charges repel each other. This gives them lots of energy. When you connect the battery into a circuit the electrons see their path to get away and take off around the circuit. When they get back to the battery they have low energy. The chemical reactions in the battery continue and force the electrons back to the anode where the whole trip starts again.

Non-rechargeable batteries have a one way chemical reaction. Given the conditions you can’t make the products of the reaction turn back into the reactants. Think about this in terms of making a cake. You can turn the ingredients into a cake, but no matter what you do, you can’t turn a cake back into its separate ingredients.

Rechargeable batteries use a different set of chemicals and a different reaction. In this situation, when you apply an electric current to the battery (instead of the battery creating the current) it flips the reaction around. The products of the normal reaction, react with each other to reform the original chemicals.

Nickel-cadmium (NiCad) batteries start with Cd and NiOOH. These react to form the products Cd(OH)2 and Ni(OH)2. These two products are converted back to the original materials when an opposite electrical potential (reverse the direction of the current) is applied across the cell.

To count as rechargeable this needs to happen safely and efficiently so that they can be recharged repeatedly.