This was a fairly rare
battery charger because it supplied not only 2 volts but also
4 volts and 6 volts. After about 1928 some radios used valves
with directly heated filaments which worked at higher voltages
maybe to reduce the drain on an accumulator or maybe the newer
filaments were longer lasting? By now the "dull emitter"
was being introduced and this didn't get as hot as earlier types
and were therefore much less stressed. Most battery set owners
had to take their accumulator to the local cycle shop which oddly
seemed the usual place set up for accumulator charging. With
the trickle charger below one could charge ones own...