A power pack unit is provided for utilization with battery-operated devices employing rechargeable batteries. The power pack unit specifically is designed for utilization with hand-held, portable cellular telephones having a removable, rechargeable battery pack. The power pack unit is physically configured to connect to the cellular telephone and provide electrical interconnections in place of the battery pack, which then is placed on the power pack unit on the opposite side, such that the power pack unit is "sandwiched" between the cellular telephone and the rechargeable battery. A supplemental power source may be connected to the power pack unit. When power is supplied from a supplemental source, the power pack unit supplies operating power to the cellular telephone and, simultaneously, supplies charging current to the battery. A cross-over switching circuit within the power unit isolates or disconnects the battery from the cellular telephone whenever external power is supplied to the power pack unit. The switch-over circuit connects the battery through the power pack unit to the cellular telephone to operate the telephone whenever no supplemental power is supplied to the power pack unit. The cellular telephone, consequently, may be operated at all times, including the times when the battery pack is being recharged.