After reading those articles carefully again it seems the Yuasa has most users votes and the safest bet. Who is the best supplier to go to or do I just head for Halfords.

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2010 XT660Z Blue, Exan can, UFO high front fender, SW Motech baseplate, heated grips, 12v point, Kevs Fuel & O2 mod, DNA Stage 2 Filter and cover, Givi tall screen, Mefo mfe 99s, Kevs throttle mod, TT high seat and 'compass'