I am also on my third battery after 6 years, despite trickle charging.
George
There is an alternative approach to this job which is considerably quicker and reduces the scale of the job itself. It is now our default approach having been successfully doing this common S1 fix for people for the last 9 years.
www.mogworksracing.com Cerealsurfer I have noted your option in my S1 file, sounds like you guys have considerable experience of this car, comforting to know.
New battery arrived today, hopefully this is the answer, at least for a while anyway. Having read Taffy and Gin's replies it does sound like these batteries, even when constantly trickle charged fail within a few years.