No, sorry, didn't make it very clear - at idle, with lights on 13.5V, at 4000rpm I get 12.5V Not what I was expecting.....
Just to put more detail in there: Electrex recommend direct connection of the positve and earth directly to the battery. I originally tried just to use the same connections as the OEM R/R but couldn't get the charge light to work. Apart form the wierd output at the battery, the bike seems to run OK. In fact, cranking speed seemed slightly higher when I fired her up.
I'm going to re-run the checks again today and get some more accurate readings, but I don;t know if this will help.......