A method for charging a battery is disclosed, wherein a constant current charging current is periodically adjusted as needed such that the change in battery voltage increases approximately linearly during the charging period. In some embodiments the charging is in three phases. An optional first phase charges with a low current until the battery voltages rises to a certain minimum. During a second phase a constant current is provided while the battery voltage is monitored. The second phase constant current is periodically increased if the rate of change of battery voltage is less than a predetermined value and is decreased if the rate of change of battery voltage is more than the predetermined value. When the battery voltage attains a predetermined value, a third phase begins wherein a constant voltage is applied to the battery while the battery current draw is periodically monitored. Charging is stopped when the battery current draw falls to a predetermined value or, in some embodiments, when the charging current drops to a value that is a certain percentage of the charging current at the termination of phase two.In one embodiment the battery voltage is monitored to determine a possible battery failure, for example in the case of the battery voltage decreasing during the constant current charging of phase two. In some embodiments the battery is shorted out in response to detection of a possible failure.