High capacity compact power source and control features

A portable charger employs metal air battery cells and has enough charge and current capacity to permit simultaneous use and charging of an attached appliance with a secondary battery. This allows, for example, a cell phone user to use a cell phone for extended periods of time. Preferably, the primary charger may have an extension cord to allow the primary batteries to be located remotely from the appliance, for example attached to a belt. An adapter provides various control functions such as voltage and current control, and a residual capacity meter. A mechanical device controls gas exchange from the primary battery.