The UM-2 battery is also called C, R14 or Baby cell.
The round battery with a diameter of 26.2 mm and a height of 50 mm is used in portable radios and torches.
The nominal voltage of zinc-carbon batteries or R14 or alkali-manganese batteries or LR14 is 1.5 volts.
Nickel-cadmium accumulators (NiCd, resp. KR14) or nickel-metal hydride accumulators (NiMH, HR14) have a slightly lower nominal voltage of 1.2 volts. Not in all case, sets can be operated from accumulators instead of batteries, as the reduced total voltage is sometimes not sufficient for reliable operation.