sounds like an excellent application for a "super cap", i.e. the very
high capacitance capacitors designed for memory backup power etc.  the
advantage being that you avoid all of the wear out and aging issues of
batteries.  in fact i plan to convert several of my computers to using
supercaps rather than batteries for pram maintenance, particularly
considering the high cost of some batteries (some being more than most
super caps).

Jinx wrote:
--------
. The batteries are just 1.3Ah, and need to supply only a
> few mAh on rare occasions. Assuming at worst 10 hours/year that's only
> 0.1% cycle. The 1k could be reduced, but for this application it probably
> would make no difference. To all intents and purposes the battery is
> simply sitting around for a few years, ready for action, until it gets
> replaced. For applications with more active cycling I'd use a battery
> monitor
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