Next set of results:
I took battery of charger. It had been on trickle for about 4 hours.
Battery 13.12 VDC
Battery to CB 13.1 VDC, 12.9 VDC a lot of rust/corrosion on CB posts.
Battery on shoreline 13.15 VDC
Cleaned post on circuit breaker:
Battery +to- and battery to either CB post all 12.89 VDC (should battery drop this quick?)
With shoreline attached battery showed 13.5 volts.
It started raining so did not get around to hooking up to truck. Quick question here: does it have to be sitting on hitch, or just plugged in?
Forgot to look at the ground post while out there.