Abstract: A method for determining time to completion is provided for a battery charging system. The system preferably includes a charger having a microprocessor and a battery with a memory. The memory includes information about the battery, including battery identifiers, charging states, charging procedures and charging termination information. The charger reads this battery and then determines the charging states associated with the battery. The charger then determines the present state of charge, and calculates a time to completion for that state. The charger then determines times to completion for the remaining charge states, optionally compensating for self discharge within the battery. A total time to completion is determined by summing the times to completion for the respective charging states.

Abstract: A battery (104) is connected to a host device (106), the host device is an electrical or electronic device, such as a cellular telephone. The battery is rechargeable, and contains a memory (110) connected to a data line (116). The battery is connected to a battery charger (102) while also connected to the host device. The battery charger detects the battery (306), reads the battery information (308) from the battery memory. The data line is common to the battery charger, battery, and host device. The charger indicates its presence to the host device by changing the voltage level on the data line (310) from a normal first level, such as a logic level of one, to a second level, such as a logic level of zero, and holds the data line at the second level. The host detects the presence of the battery charger (312) after the data line has been held at the second level for a sufficient period of time, and then may take the desired actions (314).