A PCMCIA card is provided that includes an on-board (integrated) storage battery and, preferably, charging circuitry for same. The on-board storage battery is dedicated to operation of on-board devices that have higher current/power requirements than are available from the 5 volt pins of the PCMCIA card. For example, in a cellular device application, during high-load transmit periods, the battery is used to source the power amplifier, and during low-load periods, the battery can be charged by the on-board battery charging circuitry, preparing the battery for the next high current/power transmit burst. In a preferred embodiment, the battery comprises a very thin Li-Ion/polymer battery or equivalent.