The real issue is where and how often one would need battery power.
The last three years I have camped in a field to attend an archery competition. Four days in 80 degrees, direct sun and not even a fan. The battery lasted two day before the pump was too week to trip the pressure switch.
Likewise on last year's trip to AZ, 90 degrees and no shade made TT camping impractical without a fan. I finally ordered a rechargeable fan.
A cheap generator or solar would solve part of the problem but the question is, just how much use would it get.
I might be easier to just carry another battery for a few extra days off grid.