A system for charging a battery includes an adapter, and a charger coupled to receive power from the adapter, and to provide a charging current to the battery. The charger includes a power stage with a charge pump to provide the charging current, and a feedback circuit to provide a feedback signal to the adapter. The power stage can be one of: an adjustable current source with voltage clamp, and an adjustable voltage source with current clamp. The charge pump can be implemented as a voltage divider, so that an input adapter current is multiplied by a pre-defined divider ratio to provide the charging current. The charge pump can be one of: single-phase; and multi-phase.