What is "plunging battery"

Plunge \Plunge\, n.

1. The act of thrusting into or submerging; a dive, leap, rush, or pitch into, or as into, water; as, to take the water with a plunge.

2. Hence, a desperate hazard or act; a state of being submerged or overwhelmed with difficulties. [R.]

   She was brought to that plunge, to conceal her husband's murder or accuse her son.
   --Sir P. Sidney.

   And with thou not reach out a friendly arm, To raise me from amidst this plunge of sorrows?
   --Addison.

3. The act of pitching or throwing one's self headlong or violently forward, like an unruly horse.

4. Heavy and reckless betting in horse racing; hazardous speculation. [Cant]

   Plunge bath, an immersion by plunging; also, a large bath in which the bather can wholly immerse himself.

   Plunge battery, or plunging battery (Elec.), a voltaic battery so arranged that the plates can be plunged into, or withdrawn from, the exciting liquid at pleasure.