but are they all the same kind of batteries? (I.E. deep cycle, lead acid?)
i mean with a 9 battery install you obviously know something is going right due to no voltage drops......my question to you is that after a week or so of daily driveing, do you experience a general drop in volts? .....if so this is normal due to the fact that after a week of daily driving you've drained some energy off them. That's how it was with my 2 battery setup but before long it wouldn't matter if i had charged both them up a night or 2 before, the volts would drop.
With the physics i've explained i'd experience you'd have a voltage drop or a gradual voltage drop or time with yours unless there's something else in the wiring (isolators,celinods,diods)
How often do you have to recharge your battries and what kinds are they? what types? and what powers? also what kind is being used to require 9 batteries?