whats it mean when my battery's flat, I bump start the bike and at the end of a good ride with no lights on etc, its still just as flat? Reg/rec on the way out?

No charge from the generator I'd say.

get testing!

Or your battery is just f*cked.

Get testing.

Stick a multimeter across the battery when the bike is running and no other load on the charging circuit (lights etc). 14V+ = good charging circuit and f*cked battery. <14V dodgy charging circuit and probably still a knackered battery.