To provide a quality judging method easily judging the quality of a lead-acid battery (whether the function can be recovered by charging or not) in a state of over charge, and provide a method of charging the lead acid battery and a charger.

A battery to be checked is charged by a constant current, a constant voltage, or a pulse charging, and the quality is judged based on the behavior of the charging voltage or the charging current. Namely, in the case of supplying the charging current (including pulse current peak value) by a constant current charging method, the battery of which the charging voltage drops below a prescribed charging voltage after charging for a prescribed period is judged as that with good quality, and in the case of a constant voltage method (including pulse current peak value), the battery of which the charging current value increases higher than a prescribed current value after charging for prescribed period is judged as that with good quality. Furthermore, the lead-acid battery in a state of over charge is charged by impressing not less than 2.5 V/cell and maximum voltage of 4.0 V/cell (In the case of pulse charging, the peak value is 2.5 to 6.0 V/cell) at the start of charging.

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