I have a 3kw inverter charger that surges to 6kw. I run on 4/0 cables, and have no problems running both AC's off the inverter. 15 minutes later the low voltage alarm is on, and the inverter shuts down. You need to remember an AH is not an AH. The faster you pull current from a battery, the lower the capacity you have to work with. Most batteries are rated at their 24 hour rate, a 2 hour rate looses about 1/4 the capacity.
Specifications for Concorde Sun Xtender AGM Deep Cycle BatteriesWhat are you attempting to run that requires that much power? Most rv's (other then the AC) can run quite happily off a 2kw generator. Many dry campers take only a 1kw to back up solar.