PURPOSE: To surely judge the degradation of a battery by precisely detecting the internal resistance of the battery.
CONSTITUTION: A voltmeter 6 which detects a terminal voltage at a battery 1 and an ammeter 5B which detects a charging current for the battery 1 are installed. A battery-life judgment circuit 7 judge the finish of a charging operation when the terminal voltage detected during the charging operation is raised so as to exceed a prescribed voltage and the charging current is dropped so as to exceed a prescribed value. An ammeter 5A which detects a discharge current from the battery 1 is installed. The battery-life judgment circuit 7 makes a discharge current at a value, which is different at prescribed intervals, flow to one phase of a running motor 4 via a motor-drive control device 3 after the judgement of the finish of the charging operation, it computes the internal resistance value of the battery 1 at a prescribed discharge current value on the basis of every discharge current value and of the terminal voltage which is detected at this time, and it estimates the degradation degree of the battery 1 on the basis of the computed internal resistance value.
INAGAKI MITSUO
SAKAI SHOJI
