Rechargeable battery with isolated charging circuit

A system for optimally recharging a battery cell while powering a device connected to the battery pack, in which an electronic switch (22) connects a battery pack power-output either to the battery cells (12) or to a second power-input contact (20). When not recharging, the battery-pack power-output contact (16) is connected to the battery cells (12), thereby powering the device from the cells. When recharging via a charging unit, the battery pack's power-output terminal is uncoupled from the cells (12) and coupled to a power source of the charging unit, thereby powering the device from the charging unit. At the same time, a voltage is supplied to the battery cells (12), thereby recharging them. The switching may be activated by a voltage supplied by the charging unit to a temperature monitoring thermistor (24) in the battery pack. In this way, the battery pack's power output may be automatically switched whenever it is placed in the charging unit.