" but only charges at 40 ah which seems to never peak the batteries " Is it spec'd to only put out 40A? And with what kind of voltage or regulation? It may not be topping off the batteries simply because it is malfunctioning, or not putting out the voltage they need.
If you don't need it and can make better use of the space, by all means travel lighter and sell it. But if that AC sometimes comes in handy, it might be worth looking into whether it can be made to work better. If it is simply wired up as a 6kW AC genset with a small capacity for DC, the answer may be to add a "shorepower" battery charger (or use the one you may have?) and convert the higher power AC output for charging.
Not all gensets have equal abilities on their AC and DC sides, some are designed with very lopsided abilities.