This invention is directed to a methjod for charging a rechargeable battery. In this method, the open voltage of the battery is measured and the number of cells estimated. The state of charge of the battery is then tested by supplying a controllably varying charging current to the battery and testing for evolution of gas. If no gas is evolved, the battery is charged until the voltage equals the estimated number of cells multiplied by a voltage which is characteristic of the battery. The foregoing steps are repeated alternately until gas evolution occurs. The true number of cells is then determined and the battery is charged at any charge rate until the voltage equals the true number of cells multiplied by a predetermined voltage. The battery is then charged at that voltage until the charge current decreases to a predetermined low value followed by charging at that predetermined current at any voltage for a predetermined period of time.