12 volt dc to 12 volt dc 20 amp split charger. Designed to charge and maintain a separate 12 volt battery from a 12 volt dc system. It has a three stage micro processor controlled charging system and uses voltage sensing for automatic cut in and drop out of charge from the 12 volt system, so will not charge the separate 12 volt battery until the 12 volt battery on the main vehicle is charged or being charged.