Also, it's important to note that batteries don't generate power. They store power. Literally. You pump electrons into them and they hold onto them internally

Also, it's important to note that batteries don't generate power. They store power. Literally. You pump electrons into them and they hold onto them internally until they can be released again. Think of it as a water balloon for electrons. You create a vessel which is capable of efficiently containing electrons. Then you pump electrons into it and hope enough of them stick to be worthwhile. This is battery technology. Different battery technologies have different characteristics. Nickel batteries usually have some form of "cell memory" where the cell will store "stale" electrons indefinately, and lose the ability to release them. These electrons can become "trapped" inside the battery and reduce it's capacity. Likewise the chemical composition of lithium batteries makes them extremely volatile. This means that if you were to completely remove all electrons from the cell it would forget that it is a battery and refuse to store future electrons you try to pump into it. You also have to balance each cell in a lithium pack, else they will become uneven and one could possibly become completely empty (killing the cell). Likewise, when a nickel cell loses all it's electrons it is still possible to "zap" the cell back to life with a large jolt of electrons. Some of which stick, some do not. Sometimes this results in the battery "waking up" to accept more electrons. Sometimes it doesn't, and a 6 cell (7.2v) nickel battery will have to be dissected to replace the bad cells.