Abstract: An especially low power, fast completion battery charge process varies the voltage, current, and time of charging a battery according to the battery's state of charge. Initially, a battery charger apparatus applies a fast charge current to the battery. When the battery voltage increases to a target voltage, the battery charger applies a fast charge voltage to the battery. This continues until the current flowing through the battery decreases to a prescribed minimum current. The battery charger then calculates the elapsed time between the battery's initially receiving the fast charge current and later achieving the minimum current. Using the elapsed time, the charger computes a proposed overcharge time comprising a multiplicative product of the elapsed time and a temperature-dependent adjustment factor. Next, the battery charger applies an overcharge voltage to the battery for the proposed overcharge time, unless the proposed overcharge time exceeds a prescribed maximum time.