Charging Rate of Honda 2000

Thanks for all the help. Let me just throw out a typical trip for us. Maybe that will clarify things, at least for me. When we leave the house, both 6 volt batteries are showing in the 6.25 - 6.30 range having charged with shore power. Each a/noon I will plug shore power into my 2000, and run it for about 3 hours. We use a Fantastic Fan and a small florescent night lite all night. After bfast, no coffee maker, minimal light usage etc, I check my batts. Typically they are in the 5.15 - 5.60 range. A 3 hour "charge" will bring them back to roughly 6.15. This is where the "1 volt" comes from in my OP. I was just curious how much longer it would take to get back to 6.25+ range, hence one volt. Sorry if I am trying your patience on this, but it is something that crossed my mind after a week (typical) trip.