In article ,
Clive Page writes:
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?

For smoke alarms on PP3's, I use alkaline, and replace annually.
They last longer than a year, but not 2 years, but it's easy to
nominate a date, such as your birthday, or Christmas, when you
routinely replace them.

I did buy some of the long life lithum PP3 cells, and they worked
for a year or two, but then the detectors started bleeping.
However, the batteries are 11V, so I presume this is due to too
high voltage, although I'm not sure why they worked for some time
before that.

Most of mine run off the burglar alarm supply, so there are no
batteries to change in them, but I look after various battery
ones around the family.

--
Andrew Gabriel
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