To digress the Comet starter was 120vdc. For a start it required 28vdc and 120vdc. Normally provided by a GPU. Under extremes an internal start could be carried out. The Comet had six batteries (24v) and five of these were connected in series for a start. The remaining one being used for Ignition and fire protection. In the Comet installation the switch between series and parallel was done with a truly massive wafer switch cable operated from the Engineer's panel.
Some things you never forget.
A full battery change was needed after an internal start on return to base.