This invention relates to a method for charging a rechargeable battery especially lead-acid batteries. In this method, the open circuit voltage of the battery is measured and the minimum number of cells is estimated from this value. The battery is then charged at any charge rate and at a constant current until the battery voltage is substantially equal to the estimated number of cells multiplied by a voltage which is characteristic of the battery, and thereafter the battery is charged at any charge rate and at the aforesaid battery voltage until the current decreases to some predetermined value. The foregoing steps are repeated alternatively until a constant or substantially constant value for the estimate number of cells is obtained. Thereafter, the battery is charged at a voltage equal to the number of cells multiplied by the characteristic voltage of the battery until the current reaches a predetermined value and then the battery is charged at some predetermined current for a predetermined period of time.