Herein is disclosed an improved device for supplying electrical current to a load from a primary current source. The device includes first and second rechargeable batteries each of which is coupled to both the load and the primary current source by a circuit. The circuit is configured to supply the load by cyclically drawing current directly from the batteries one at a time. During each cycle, the circuit draws current from one of the batteries while simultaneously recharging the other battery which with current from the primary current source. The circuit is configured to switch the drawing and recharging of the batteries at the end of each cycle. The circuit is further configured to set the cycle for a period of several minutes.