Battery Condition Meter
Essentially a voltmeter which records the voltage output of the battery, from which can be gauged the battery's overall condition and any problems in the electrical system. The theoretical voltage of a cell is 2v but this can rise to as high as 2.7v during charging. When taken off charge, the cell will register 2.1 volts for a while and this will gradually fall to 1.8v when the battery is fully discharged. Voltage scales on a battery condition meter show the extremes of voltage readings and a centre band indicates when the battery is functioning properly. If the register needle falls consistently outside this permitted band, it indicates a fault in the battery itself or possibly in the charging system.
Also see: How it Works - The Battery