A plurality of serially connectable lithium based batteries provide power to a load upon actuation of a user operated switch. Upon actuation of the user operated switch, additional switches intermediate adjacent batteries close to serially connect the batteries to one another and a load. A signal from the load maintains these additional switches closed. A charging circuit is associated with each battery to charge the batteries in parallel upon opening the additional switches. Sensors for temperature, current and various other parameters provide signals to one or more controllers to prevent damage upon the presence of a fault indication signal.