Charging circuit – batteries – inverter

[hippieforever3]

I've had the 4 12 volt batteries individually checked and they are in
reasonable health.
The generator is putting out enough AC to be able to run all three AC
units.

However when I try to charge the batteries only with the generator, I
can barely get the batteries charged to 11.5 maybe sometimes with a
tailwind,12volts. Never the same 12.5-13+ I can get running off the
alternator. Just for fun I've charged the batteries off a jump from
the toad and I can get 12+ in 15 minutes or less.

Does the stock charger limit at 12 volts?
Is the output voltage adjustable? How?
Does anyone have a schematic of the stock charger? I can probably
modify it, if I can get a schematic.
If not, has anyone replaced the stock charger with some after market
smart charger? Recommendation? Has anyone put a bank of 6 volt golf
cart batteries in the compartment?

I'm planning on adding some solar panels. Has anyone installed a
smart charger – inverter – solar panel controller that they are
REALLY happy with?

I'm assuming those two large aluminum boxes in the port-side
compartment are the charger and inverter with circa 1980s electronics
and that the two (in my case unmarked poorly electrical taped) leads
out are the house 12 volt and 120 volt circuits ... Correct?

I just can't get any reasonable performance out of my existing
system. I drop a volt an hour with minimal house lights.

Help I need suggestions.

Movin on,
GPSGary – Morro Bay State Park
1984 FC 35