NEVILES AUTOMATIC BATTERY SWITCH, 1938

The switch is connected between a large power supply and a rack of batteries to be charged (usually lead acid). The large coil will release the armature when the batteries are fully charged, this will be when the current to the batteries is low enough to release the armature to the coil, the arm will rise at this point removing the fingers which are dipped into two cups filled with Mercury and will interrupt the current to the cells of the batteries.

Bruce Hammond Collection

A1573