The charge evaluation system uses the measured voltage during operation of the IC engine starter motor and the measured battery temp. The dead point timing of one of the reciprocating pistons is detected and the voltage at this point is recorded for conversion into a value characteristic of the battery charge.Pref. the dead point timing is determined by monitoring the current provided by the battery (13) which is differentiated, the battery voltage being recorded when the current characteristic exhibits a relative extreme value, or a turing point. The charge measurement is terminated in accordance with a given criteria, e.g. elapsed time or a defined engine revs.
