I don't want to drag anything off-topic, but I feel like I am misunderstanding something somewhere and wanted to see if someone could clarify.
When you are talking about charging voltages, are those with the panels connected, or unconnected? I just got a little 2W trickle-charge panel to keep things topped off, and in good sun I measure the output straight from the leads at 17v - 20v. As soon as I attach it to the battery bank, I see the overall voltage in the system read whatever the batteries were putting out on their own.
I understand that you need a higher voltage going into the system to charge the batteries, but it's not clear to me if that's happening or not. When you are talking about the 13.3v, is that what the panels must be producing independently, or is that the level to which they have to energize the entire sytem when they are connected in order for any charge to apply?
I ask mostly because the trickle charger doesn't seem to be working; if I leave it hooked up for a day, the overall voltage reading in the system seems to be lower at the end of the day than it started out (this is without going into darkness at all; the panel has a regulator which is supposed to prevent it from bleeding juice out of the system at night, but I eliminated any potential problems with that component by only connecting and measuring during daylight hours).
If it's the case that the panel has to bring the whole system up to 13.3v to charge, then how exactly do small trickle chargers ever work on larger battery banks? I've only got ~200AH of capacity in my house bank but it doesn't seem all that large, and they market these trickle chargers as being able to keep your car, boat, or RV 'topped up' when not in use. I'm confused as to how that happens, I guess, or if it's simply untrue and you need really massive panels to see any sort of charging at all.