We did this years ago. Have a battery box with a couple Optimas for our (non RV) tailgate.
Way back in 2004, I used a battery with power inverter to power a receiver. Non-rv tailgates really don't need generators.
I’m an RV moron but camping/backpacking gear nerd. It seems like the tech is rapidly improving in most metrics. Probably someday the generator noise issue at tailgates will solve itself is my guess.
The units I’m thinking of can’t be bigger or heavier than a generator but maybe they don’t get job done or maybe the hardware costs 3x.