IIRC, the Sea King didn't have a battery hot light: if so, it didn't bl**dy well work! November 1973, Bay of Biscay, dark and dingy night off RFA Olna on CASEX when we smelt "something electrical". As always, life wasn't meant to be easy, and Olna had a radio failure, so our pleas to come home fell on deaf ears. We went through a full ditching brief, UC at the hatch to the avionics bay with fire extinguisher, all non essential electrics turned off, and we got back to Olna it was to find the other SK on the flight deck, preventing a landing
Anyway, when we landed the battery (just forward of the two pilots, for those not familiar with the Sea King) was so hot, the black hand gang couldn't disconnect it. So they promptly cut the battery cable with bolt croppers, rendering the cab U/S for longer than it took to replace the battery
At the time, we had no idea that it was a thermal runaway, and we were obviously very lucky not to have it blow up on us.
Although NiCads have their attributes, I am more inclined these days to use lead acid batteries, with many of the new generation coming quite close to NiCad for performance. Cost wise (as an owner) they are much cheaper to operate than NiCads, and have less down time considerations: plus, no propensity to thermal runaways as with the Nicads
