I don't like generators for charging batteries. Nothing personal but it has to do with battery and human chemistry. A lead acid battery that is discharged can take 5 hours of bulk charge just to get back to 70% of capacity. It can take another 5 hours to get to 100%. If you don't always get back to 100% you harm the life of the battery in that it will begin to get comfortable with less than 100% and eventually refuse to take a 100% charge.
This means that for proper battery maintenance you'll need to run your generator (any generator, no matter the output capability) for at least 10 hours. This is where the human chemistry rubs against the battery chemistry, causing a high degree of friction. Nobody wants to run a generator for 10 hours at a whack. You could run it for, say, 3 hours a day but this won't be likely to get you back to full as quickly as you're consuming the juice.
The dilemma is that for most of this 10 hours you're not pushing in a whole lot of current but it's still essential for the chemistry and you have to do it with a generator that is either on or off no matter what it's putting out.
Personally, I think a solar system is better or possibly a hybrid (part generator, part solar) because it can supply something as long as there is light. Solar is far better at supplying sustained current even though it may be low current.
There is a great treatment of this at
Battery University if you want to learn more.