Okay my bass is getting picked up on Friday 1st May by FedEx to be delivered to Sims LEDS.
It is getting fitted with 11 LED's(2 at the 12th fret) with magnifier lenses and a toggle switch to operate them.
He uses the same battery within the cavity to power them as they are very low current drain, things have improved since he began this company as he used to route a new cavity and place a brass plate over the compartment as the first ones he did used 18V.
I asked plenty of questions on this, he said that the LEDS's act as an battery level indicator as they will go dim before the current dies completely to not supply the pre amp.
He has done this on loads of instruments and has had no complaints.
I shall post pics as soon as I get my bass back