I'm sorry but that's not the true. The battery is die all the sodding time.

When I worked in an office I used to switch the magic mouse off anytime I wasn't actually using it. Going to the toilet switch the mouse off, going to get a drink switch the mouse off, somebody comes over to talk to me and I don't need to use the computer switch the mouse off. All this just to extend the battery life.

I then replaced it with a generic Bluetooth mouse that uses one AA battery, and I've had it for over 2 years at this point and never needed to replace the AA battery. So either lithium ion has less storage capacity than a chemical battery or the magic mouse has a teeny tiny microscopic battery.