A battery charging circuit sets charging current according to either the capacity of the battery under charge or a constraint of the charging source, depending on the properties of the charging source. The battery charging circuit sets termination current, however, according to the capacity of the battery under charge, regardless of the properties of the charging source. For example, the termination current may be set as a fixed fraction of the recommended C rate of the battery even if the charging current supplied by the charging source is below this C rate. Always setting the termination current in proportion to the battery's capacity permits detection of the current at which charging should terminate even when the charging current is constrained by the charging source and no longer depends on the battery's capacity.