Abstract: A battery management system maintains a charge on at least one. auxiliary battery by switching the auxiliary battery automatically into parallel with the main battery charging circuit or with the auxiliary load. The system uses the AC component of the charging signal of a vehicle or boat charging system to trigger switching circuits coupled to operate relays or similar switching means which couple the auxiliary battery to the main charging circuit. When no charging signal is present, i.e., when the vehicle or boat engine is turned off, the auxiliary battery is switched automatically out of the charging system and is charged and in condition for use. A delay circuit can be provided for providing non-shorting operation, especially for use with more than one auxiliary battery which batteries are charged in parallel and loaded in series, whereby the combined series voltage of the auxiliary batteries would exceed the vehicle or boat supply voltage.

Abstract: A battery management system maintains a charge on at least one auxiliary battery by switching the auxiliary battery automatically into parallel with the main battery charging circuit or with the auxiliary load. The system uses the AC component of the charging signal of a vehicle or boat charging system to trigger switching circuits coupled to operate relays or similar switching means which couple the auxiliary battery to the main charging circuit. When no charging signal is present, i.e., when the vehicle or boat engine is turned off, the auxiliary battery is switched automatically out of the charging system and is charged and in condition for use. A delay circuit can be provided for providing non-shorting operation, especially for use with more than one auxiliary battery which batteries are charged in parallel and loaded in series, whereby the combined series voltage of the auxiliary batteries would exceed the vehicle or boat supply voltage.