A rechargeable storage battery power supply system in which a coulometer is used as a logic device to provide transition between high charge rate and low charge rate. During battery discharge, the coulometer may act as a logic device to disconnect the load from the battery after a predetermined time integral of current is drawn from the battery. The charging current is applied in reverse direction through the coulometer and when the coulometer reaches its high impedance state in the charging direction a trickle charge is bypassed to the battery. The trickle charge control includes a thermistor responsive to battery temperature. An additional circuit is provided which acts to provide constant voltage float charge after the battery has been fully charged, and which additional circuit also uses the coulometer as a logic element.