Batteries, even leisure batteries are not made to be charged and discharged as often as we use them. In a caravan or on a boat they may be used for a couple of weeks at a time, where as we are using them constantly over a long period. I have came across a problem with my batteries and all they need is a very long charge on an old fashioned type charger that doesn’t cut out when the battery is fully charged.
The modern chargers get a full signal from the battery and stop charging even although the battery is not fully charged, and after giving it a good charge with the old fashioned charger it brings the battery back to working fine.
I don't know if the explanation is correct as it was someone else who told me, but I know for a fact that it does work.
Peter Fogwill
www.window-tools.com