On Friday, 16 March 2018 14:10:46 UTC, 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 don't think so. ZnC/Cl leak when flat too.


NT