Passive to active wiring

[Booster Menz]

Hello. I just got a hammer bass guitar from a friend and I realized that the bass sounds so low even through an amp. He told me someone rewired it from active to passive due to battery issues.
How do I rewire it back to active. It's a 4 knob bass; volume, blend, treble and bass as well as a G&B 2 band preamp in it. Thanks. The circuit currently looks like this.

 

[GIBrat51]

Well, first of all... welcome to Talk Bass. Next; you might want to post your question in the "Pickups and Electronics" forum. Those guys live for stuff like this, and can tell you much more than I ever could; I'm not really familiar with active wiring at all. I imagine, though, that they will ask you if you know exactly what the "battery problem" was/is. That will have to be dealt with first. Good luck with it - and, again; welcome!