Abstract: A personal computer of this invention has a battery pack mounting section for detachably receiving battery packs having different current capacities. The personal computer also includes a switch mechanism for detecting whether a battery pack has a high or low capacity. Battery characteristic values consisting of charge and discharge voltage/current characteristics in units of batteries are prestored in a memory in a power control CPU (PC-CPU). The PC-CPU refers to the memory on the basis of capacity data from the switch mechanism and reads out the corresponding battery characteristic data. A power supply circuit performs optimal charge control on the basis of this characteristic data. Two battery packs are prepared. When the PC-CPU detects that the currently used battery pack is in a low-battery state, it selects the other battery pack to supply the operating power to the personal computer. At the same time the PC-CPU performs optimal charge control of the battery in the low-battery state.