The function of an RV generator is to charge the battery bank or use it directly as a power source to 120 volt AC outlets. (TV, microwave, air conditioner, furnace etc...)
If you use it to charge the battery bank, be aware that it is not a very efficient method at all. Most RV generators charge batteries through the converter charger and you do not get the full output capacity of the generator, being limited by the amperage of the converter itself.
Some generators do have a DC output (12 volts) but this method is not recommended as it has the potential to damage your batteries due to not having the voltage regulated. The resulting erratic amperage applied leaves a lot to be desired.
Sometimes the best option is to use a good quality inverter plugged in to the generator with an actual battery charger plugged in to the inverter. it. It will work more efficiently and result in better charged batteries in a much quicker time.
We are always available for expert advice and information.