The ignition protected Digital Voltage Sensing Relay can be surface or panel mounted and allows the charging of a second battery from a single charging source. When the voltage on the start battery rises to a level indicating a 60% charge, the VSR engages allowing the 2nd battery to charge. When charging stops and voltage falls the VSR will disengage isolating the two batteries from each other isolating the starting battery from the house bank. Dual sensing functionality enables the sensing of two battery banks allowing two way charging.