Abstract: Apparatus for indicating the charge condition of a secondary cell, comprising an integrating device which progressively sums the ampere-hours drawn from the cell, and a computer which is programmed to provide a voltage output whose magnitude indicates the total number of ampere-hours available, from the battery at the particular discharge current and temperature. A comparator subtracts from this a voltage derived in accordance with the output of the integrating device. The comparator output thus indicates the remaining ampere-hours available to be drawn from the cell at the prevailing conditions of discharge current and temperature. There may be provided a further computer which is programmed in accordance with the variation in minimum ampere-hour requirement of the cell to ensure that a particular load, e.g. a starting motor, can be successfully operated at various temperatures.