And the answer is.... YES!
2 8D's and Heart Inverter fit snugly in the the locker just aft of the head. No opportunity to put battery boxes in as well though. (There's no requirement that says Thou shalt store all batteries in a battery box, is there?)
This opens up two great lockers - one at the head of the quarterberth - which used to house a battery and inverter and one beneath the new nav station seat... Excellent! :-)