Originally Posted by 3 Dog Nite
You'll find that charging the batteries with generator takes a long time if their power is low. Maybe 12-15 hrs. I start the engine & let it idle around 1000 rpm for 1 hr. This uses the alternator to charge them much faster while using less gas.
The charge time depends on your converter and what charging algorithm it uses. My WFCO will charge my 4 grp 27 coach batteries from 50% charge to 90+% in about four hours.
I went through several alternators until I figured out that they were being burned out by running at full load for long periods. Now that I have a 220 amp alternator I have not had any problems.
I have a friend with a 40' diesel motorhome with a 120 amp alternator, his owners manual says that if you are going to start driving with discharged coach batteries you should run your generator to avoid burning out the alternator.