I can buy a generator for less than $100.00 that will charge my battery in just a few hours. It will charge it when it rains, it will charge when it is cloudy and it will charger it in the shade.
The generator will be noisy, smelly, require me to carry extra gas and give me one more piece of junk to haul around and maintain.
When I want to truly camp it involves a canoe and a tent and a remote location. Unfortunately those trips are rare. Usually I am RVing with the public with whatever conveniences the CG provides.
Out West, boon docking on public land was common. Here in the Midwest less so.
All of this of course is just my opinion but in answer to the OPs question, my choice would be an inverter type generator of about 3 KW.
It will be about as quiet and efficient as any.