Abstract: A flexible battery case with an insert mating to the tongue and groove joint to provide a stable platform for the controls, displays and peripheral connectors. Other connectors are disposed within a plastic housing and overmolded to create a waterproof seal. A charger is configured to execute a software program to confirm charger authorization to enable secondary battery charging and discharging. The control system is configured to monitor the integrity of a heating element and executes a software program to disable charging if the integrity of a heating element is compromised. A flexible substrate has a PCB on one side, and supports the individual battery cells and surface mount circuit boards on an opposite side. The flexible PCB substrate may be folded to sandwich an insulating layer therebetween.