Car Battery

[andywhy]

powerandtorque is spot on about a discharged battery dying quicker (having a shorter life). It's a chemical reaction called sulphation and occurs when the battery is under 100% charge. The lower the charge level the quicker it occurs. Eventually it becomes so bad that the battery won't hold a charge sufficient enough to start the car. So if you don't use the car often or plan not to use it for a while it's best to disconnect the battery to save it discharging.