I have a 200ah Invicta slim line lithium battery in my hilux, and a 2000w Redarc inverter.
Expensive set up at around $2000aud a piece but the battery for eg has a 7 year warranty.
I use this set up to charge my husky batteries and I don’t worry about draining the aux battery. 200amps of lithium is a lot of power, essentially equivalent to 4 lead acid batteries of a standard size. lithium you can drain to around 10% with no voltage drop
Also have a solar panel on the roof of the Ute to help keep it topped up.
Do a bit of research into lithium batteries as I think that is the answer. Another benefit of lithium is it charges quicker than lead acid, so you don’t need to drive as far to replenish it. I have a 50amp DC-DC charger so essentially 1 hour drive puts in 50a, but you can add multiple dc dc chargers to increase the charging speed.
Petrol generator to charge the batteries seems. a bit counter intuitive 😂