Bought a guitar with a Fishman Fluence and a sustainiac and have a couple questions.

Will one battery power both pickups? I know there's a separate compartment for the sustaniac, but does that power the pickup part of it or does it only power the sustaining part? So say the sustaniac battery dies, can I still use it as a pickup just no sustain function or can I not use the pickup part?

The guitar has clip-in battery compartments. If I were to buy a fishman fluence battery pack, could I just put it in there without having to drill a hole at all? And would it be easy enough to just take out of the battery compartment and charge it, assuming I don't use adhesive to attach it? Or if it does fit, would just letting go loose be a bad idea? Or alternatively, would a rechargeable 9v battery be good? I was thinking about those but from the little I found it doesn't seem to be a great idea? Not really sure tho.