Ah. That's better! Don't know what I'm doing wrong - two lengthy replies haven't appeared. I'll be brief this time just in case.
Simon; thanks for the tip, I'm now watching it and will have a go.
Roy; thanks for the offer of a rebuild, but I'll stick with lead acid for the time being. You are right by the way - I'm a retro geek, but I do upgrade bulbs to LED types, so not a total luddite.
Graigfawr; yes please! If it holds charge I would like it. We can agree a price and I'm quite happy about the postage.
Thanks guys, Colin.