PURPOSE: To recover the original capacity of a lead storage battery having insufficient capacity due to a drop in the temperature of electrolyte.

CONSTITUTION: A temperature sensor 3 is provided with a lead storage battery 1 for forklift charged with an on-vehicle type charger 2 for forklift to measure the temperature of electrolyte from Saturday morning in winter until Monday morning through Sunday, a holiday. When the temperature of the electrolyte decreases as low as about 10 degrees C at Sunday midnight, a temperature controller 4 and a calendar timer 5 are actuated. The on-vehicle type charger 2 for forklift is automatically operated from Sunday midnight until Monday morning to recharge the lead storage battery 1. Thus, the temperature of the electrolyte in the lead storage battery 1 will increase as high as about 35 degrees C after exceeding about 30 degrees C, the temperature which can recover battery capacity up to 100%.