PURPOSE: To suppress the performance reduction accompanying the advance of cycle by adapting also the charge control for detecting the temperature rise in a specified part of a synthetic resin battery jar wall surface or an electrode terminal, and ending charge, other than the control by battery voltage.

CONSTITUTION: While the temperature of a part with a height 1/2 or more of a battery jar wall surface is measured, its output signal is transmitted to the control part of a charger. When the battery temperature is less than a set value 1, then, charge is started to start a timer, and when the temperature is the set value 1 or more, the charge is still stopped. It is continuously judged whether the temperature is less than a set value 2 or not during the charge. When the battery temperature is raised to the value 2, the charge is stopped regardless of the timer, and when the temperature is not raised to the value 2, the charge is stopped by the end of the timer. Thus, in the battery, performance deterioration such as reduction of electrolyte by overcharge or reduction of discharge capacity can be suppressed, and a proper state can be kept.