On Friday, 6 April 2018 15:05:34 UTC+1, Dave Plowman (News) wrote:
In article ,
newshound wrote:
Going slightly OT, pulled an apparently dead 105 AH leisure battery out
of a caravan yesterday (hadn't been used for months and the charging
circuit claimed it was dead when on mains hookup).

Gave it best part of a pint of demin water and stuck it on charge on a
traditional charger, this morning all the cells are bubbling nicely and
it's showing over 14 volts immediately after disconnection. Will stick
it on a smart charger for a few days but I'm quite hopeful.

Sadly, voltage is no real check for a lead acid. You need to measure its
capacity in amp.hrs. No real point in keeping a thumping great 100
amp.hr battery if it's well down.

I thought the only way to estimate the charge in a lead acid cell was to test it Specific gravity or similar with a hydrometer, well this is what I was told at school when given the job of charging their lead acid cells for physicas experiments.