In article o.uk,
Dave Liquorice wrote:
I'm only quoting this FWIW as it's not my experience. I have a clever
electronic battery tester which works out the actual capacity and that
shows nearer 20% per month.

I'd say even that is high, no doubt that also includes the energy
taken by the tester.
Dunno exactly how it works but I suspect it puts on a very heavy load for
a fraction of a second only. I checked its reading against a 5 year old
battery by doing a 20 hour rate test - and it was spot on.
Lead acid batteries have a very low self
discharge, Battery University say 40% per year (3%/month average):

http://www.batteryuniversity.com/partone-6.htm

Dunno how the slope of self discharge goes, though.

--
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Dave Plowman London SW
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