not a busa but a 07 gsxr 600 with problems need advice

[k03gsxr750]

Rectifier/Regulator is a very very common problem on that year bike. Sounds like a stator if the voltage goes down when revved

+100
I've sold bunches of those.

[lankeeyankee]

If the battery was in the shop for awhile and they drained the battery low they may have collapsed a cell which causes an enternal short on batteries,
Sounds almost like it.