In the days when having a valve "wireless" meant periodically puchasing an expensive High Tension battery of maybe 90 or 120 Volts and regularly taking your 2 Volt lead acid accumulator to the local radio shop or garage for recharging, it was necessary for the owner to have a means of establishing if the poor performance of the radio was due to "flat" battery or something more serious. The two examples here are typical of many which were available in the 1920's and 1930's. Both instruments are of the moving iron type.
Battery testing Pocket Meter chrome case with cardboard box DC 0-12V 0-120V working foreign
Battery testing Pocket Meter chrome case in imitation leatherette covered wooden box DC 0-12V 0-120V working foreign