A multiple battery system for a vehicle comprises a primary battery; a reserve battery electrically connectable to the primary battery; and a control unit with a relay switch electrically connected between the primary and reserve batteries. The relay switch is operable to close upon actuation and connect the reserve battery to the primary battery. The control unit also has a receiver electrically connected to the relay switch and is adapted to receive a control signal for actuating the relay switch. A wireless transmitter has a manually actuable switch for sending the control signal to the receiver. With this arrangement, actuation of the transmitter switch causes the control signal to be transmitted to the receiver and actuate the relay switch to connect the reserve battery to the primary battery.