Well, in the end I decided to fit the Odyssey PC680 from
Knights Batteries which does deep discharge, can retain a full charge for two years, AND gives out mega power compared to the standard rubbish. This battery was delivered next day, as promised, and cost me £90 all in. Now bear in mind that the standard lump is £50 odd, and is ****e even when new on a full charge, and is usually shot within a year or two, and the Odyssey becomes good value. That and it comes with a 2/3 year guarantee. It's fractionally narrower and you have to straighten the connector tabs, but apart from that it's a direct bolt on. The bike whizzed into life on the first click which it has never done before.
Top, top job, and i can't recommend it enough! Well impressed.