Charles & Sandra Cohen
I had an IC-706mkIIg (the predecessor to the IC-7000) on my boat.
It was quite happy running off batteries. But they were _big_ batteries -- four Group 24 (car-starting-battery size), 6-volt, deep-cycle batteries, in series/parallel.
I used 6-gauge wire between the batteries and the rig, to minimize voltage drop during transmit. The IC-7000 draws 20 amps at full power, and the voltage drop, with smaller wire, can be substantial.
. Charles VA7CPC