Yamaha BB-G5A: 9V -> 18V

I've been cruisin a bit through the forums and the general consensus for EMG pups is that 18V is pretty much the way to go.

My question is, will the preamp circuitry hold up to the extra voltage, I've heard that the EMG circuit definetly can and that most others 'should' be able to take up to about 36V but I don't feel like blowing a preamp just cause I was too hasty.

On the chip on the board are the numbers/letters:
4558D
JRC
1053J
So if anybody know anything about the chips and their capabilities, I'd be very grateful for any information.

I'm going to go along the lines of the three battery clips method of setting it up. I have a problem on account of Yamaha, being Japanese, are really good at making things small and have got an absolutely tiny cavity, theres barely room for all the wires, let alone a battery. Plus it has a quick-change compartment. So I was thinking of seeing if I can buy another door for the cavity, drill a hole through it and have a battery pack that I tape to my strap or pants or something.

Would it be worth it, I'm kinda bored of not being able to do anything (ie start my bass) due to lack of funds, so I want something quick and cheap that I can do to make this one sound different.

I have searched the forums but I didn't find anything specific to my bass (almost had something on an RBX-765 though, which is pretty much the same).

Can I expect much/any difference in my tone?

Josh D