Abstract: A hand-held data-gathering unit is formed by removably connected control and power modules: The control module contains a keyboard, a display device, a data input probe, and a microprocessor. The power module contains a rechargeable battery with a converter and associated power logic, and a memory system with associated memory control logic. The hand-held unit has a normal low-power standby mode which is maintained during the absence of input data from either the keyboard or the data probe, and an operation mode which is initiated by the arrival of input data. During the operation mode, input data enters the control module and is forwarded to the memory in the power module. As data is gathered during portable operation, the memory may reach capacity or the battery voltage may drop, or both. The power module may be removed from the control module and replaced by a fresh power module with a fully charged battery and an empty memory.