A method for supplying electrical power for operation of a device that includes at least two rechargeable batteries, the device also including both at least one buck DC-DC converter and at least one boost DC-DC converter with each DC-DC converter respectively having a power input that receives electrical power supply for DC-DC converter operation, the device further including a battery charger circuit that receives electrical power from an electrical power source that is located outside the device, the battery charger circuit having only a single lower charging voltage output for supplying recharging electrical current to the batteries when the battery charger circuit is connected to the electrical power source, the method comprising the step of connecting the batteries in series with: a. the series connected batteries being connected to the power input of the boost DC-DC converter for power supplying the operation thereof; and b. one of the series connected batteries being connected to the power input of the buck DC-DC converter for power supplying the operation thereof; and the method comprising the additional steps of: a'. when the battery charger circuit is connected to the electrical power source, connecting the batteries in parallel and the parallel connected batteries being connected to the power inputs of both the buck DC-DC converter and boost DC-DC converter; and b'. when the battery charger circuit is not connected to the electrical power source, connecting the batteries in series with: i. the series connected batteries being connected to the power input of the boost DC-DC converter; and ii. one of the series connected batteries being connected to the power input of the buck DC-DC converter. a. the series connected batteries being connected to the power input of the boost DC-DC converter for power supplying the operation thereof; and b. one of the series connected batteries being connected to the power input of the buck DC-DC converter for power supplying the operation thereof; and the method comprising the additional steps of: a'. when the battery charger circuit is connected to the electrical power source, connecting the batteries in parallel and the parallel connected batteries being connected to the power inputs of both the buck DC-DC converter and boost DC-DC converter; and b'. when the battery charger circuit is not connected to the electrical power source, connecting the batteries in series with: i. the series connected batteries being connected to the power input of the boost DC-DC converter; and ii. one of the series connected batteries being connected to the power input of the buck DC-DC converter. a'. when the battery charger circuit is connected to the electrical power source, connecting the batteries in parallel and the parallel connected batteries being connected to the power inputs of both the buck DC-DC converter and boost DC-DC converter; and b'. when the battery charger circuit is not connected to the electrical power source, connecting the batteries in series with: i. the series connected batteries being connected to the power input of the boost DC-DC converter; and ii. one of the series connected batteries being connected to the power input of the buck DC-DC converter. i. the series connected batteries being connected to the power input of the boost DC-DC converter; and ii. one of the series connected batteries being connected to the power input of the buck DC-DC converter.