Kawasaki Er-5 Battery Issues

[benny3008]

Hi all, I have a problem with the battery draining on my Kawasaki ER-5, All started when I pulled over one day, and the bike wouldn't start again. got jump started no problem, rode home, left it charge for a while, switched off and again would not restart. Put battery on optimiser and put it back on the bike, started fine now. couple of days later after a few uses, the bike wouldn't start under it's own power again, but will jump start fine. changed the Reg/Rec for a second hand one, this overcharged the battery and cooked it, replaced the battery and put old Reg/Rec back on, ran fine until battery drained, once again, the battery will not charge and will only start from a jump start, once the jump leads are removed, bike will carry on running until either the lights are switched on or the choke is moved (in the direction which makes the revs slower, cant remember if that's opening or closing.) at this point the bike instantly cuts out and will not restart until jump started again. When the problem first started the bike would just click when attempting to start under own power but now it does nothing, no lights, no noise, nothing. Anyone got any suggestions as to what is causing this, i'm pretty sure I need to replace the Reg/Rec for a new one but any ideas welcome before I spend £70 on a new RR.
TIA