In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.

They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to make
it more compact, I'd guess.

--
*"I am " is reportedly the shortest sentence in the English language. *

Dave Plowman London SW
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