I use my 2KW Honda Type generator where the trailer SHORE POWER CABLE is connected directly to the generator 120VAC receptacle using a RV30A-15A adapter at 8AM each morning during breakfast. Then my ON-BOARD Smart Mode PD-9260C Converter/Charger can re-charge my 255AH Battery bank in a quick three hour generator run time to its 90% charge state.

This will allow me to do this all over again for the next day/night run off my batteries. I can do around 12 or so 50% to 90% charge cycles before I must do a full 100% charge cycle which will take around 12 hours or so to run the generator. Otherwise I will harm my batteries.
Three hours is about the minimun time you can re-charge a DEEP CYCLE Battery to its 90% charge state. You can use a stand alone smart mode battery charger like the Black and Decker VEC1093DBD 40AMP charger plugged into your generator and do the the same thing.
The rule of thumb is to have 14.4VDC at around 18-20AMPS available DC Current for each 12VDC Battery in your battery bank if you want to re-charge in a quick three hour time span.
This is what works great for me... I am usually at a camp site here on East side of the US that has generator run time restrictions in place so getting the batteries re-charged real quick when allowed to run my generator is what I have deal with each day.
Roy Ken