Power cut this afternoon about 1700, text from DNO saying High
Voltage fault off until 2030. Drag out generator, battery utterly
flat. Pull started the (diesel) generator and power came back about
1900. Even after that couple of hours the battery didn't have enough
umph to engage with the starter ring. It sits at about 11.5 V, one
end cell looks a bit low one electrolyte and the case at that end is
slighly bulging. Battery is kept on genset in the unheated garage so
may well have got frozen. Perhaps not last winter but in 9/10 or
10/11 it got below -10 C without much trouble.

Pretty sure the battery is a gonner and I'd not trust it anyway for a
semi-critical system. It'll be replaced but how to keep the new one
in good condition for years with it doing basically nothing. The
genset might called into service in anger once a year and
occasionally if it's "a while" since the last in anger run I'll fire
it up for a couple hours powering a fan heater to make sure it still
works.

So how do you molly codle a lead acid battery that doesn't get much
use? Keep it somewhere a bit warmer? Would have to have an easy to
use plug/socket capable of carrying the starter current. I don't want
to be fiddling about reconnecting the battery in the middle of the
night, by torch light, whilst being battered by a gale and driving
snow...

Don't fancy the idea of having it on a charger all the time, even one
of the clever ones that drop to a "float" charge. I suspect that rate
will still be too high and dry the cells out over the months.

I have got a small PV panel that I had used with it before but wasn't
convinced that the dark/low light leakage drained more from the
battery than was put in by the PV. The PV panel was in a north facing
window so not ideal. To get south facing wuld require a rather long
cable run, proably not far short of 50m by the time you've gone round
things.

Any other suggestions?

--
Cheers
Dave.