Clive Page wrote:

While lying awake last night I heard short beeps at long intervals, almost
certainly a smoke alarm trying to tell me its battery was low, but I
couldn't be bothered to get up to find which one (of two) it was. In the
morning, by some variant of Murphy's Law, the beeping had stopped but both
worked perfectly well when I pressed their test buttons. Both have PP3
batteries currently showing about 8.5 volts, so I've still no idea which
one it was, but I'll replace both to be on the safe side.

Although manganese alkaline batteries are better value for most things, I
have a vague memory that zinc chloride ones actually last longer for very
low consumption tasks, such as door bells and smoke alarms. Is this
right?



I remember that being the received wisdom, but the specified shelf life
of alkaline batteries seems so long ahead nowadays that I wonder if it
is (still) true?



--

Roger Hayter