Abstract: A battery cartridge has a communication terminal from which control signals are sent to a charging adapter to deliver various pieces of information necessary for electrically charging the battery cartridge, such as charging stop information, capacity information, full charge information, battery defect information, and so on. Different kinds of charging modes can be distinguished by detecting a property curve of a charge voltage or a charge current input to the battery cartridge. In this manner, without reducing the whole number of pieces of information, the number of control signals from the communication terminal can be reduced.