I think this battery has passed its time, my dad had it for years before me in a motorhome, but has been good up to now. Its a numax, and i notice that when i look in the cells, cant see any water. probabl;y too late, but can i put pure water in the cells, to just cover the visible bits, and then use it half hour later? have just had it charging all night, it has been cleaning a couple of houses and then dying, treading 11.8 or so, but then an hour or two later you measure it and its gone back up to 12.5 but not able to work, strange.