An automotive battery charger, which is used to charge the main battery of a vehicle, usually features at least two levels of recharge. The main recharge function is used to recharge a flat battery in a relatively short space of time. The trickle charge function is used to maintain peak battery performance of an already charged battery. For example a vehicle which is in storage for an extended period of time might be placed on trickle charge to ensure that the battery level remains constant. Most car battery chargers have automatic cut-off relays as a standard safety feature.