From memory, the Rover clock does not 'tick' in the normal way; but the noise we hear is the escapement weight being lifted, so that as it runs down the clock works. One loud 'clunk' instead of a series of 'ticks' that a normal clock sounds. it is a mechanical clock that is would electrically, and we hear the winding noise.
Electrically, it takes a single very short pulse of power from the battery. Somebody measure it as 200mAmp for a fraction of a second, maybe once every 10 seconds. A 50AH battery would supply this power for ever, or until it self discharged..
"AT 50 mph the loudest noise is the clock ticking," was the Autocar/Motor road test. RR response was "We must do something about that clock."