hour
Observer
To know if the battery is really fully charging, you need to track amps in/amps out and time.
That's not odd at all. That's one of the effects of surface charge.
I suspect your original battery might have been A) not a true deep cycle design to begin with, B) sat around at the dealer not fully charged and was already partially sulphated when you bought it, C) not properly maintained, D) all of the above.
Cool, planning on getting a battery monitor for this new setup to satisfy curiosity, but in thinking more about your third point here, there was definitely something squirrely with the battery. The fridge cycles properly and I actually ran it on the load out of the charge controller, so I know the amp draw isn't something absurd. Fridge beeping before midnight while battery was floating until sunset, while properly cycling... just doesn't match any experience I've read about over the years.
Thanks for the surface charge clarification, and your help in other thread. I owe you one! Will just throw the 6v gc batteries in and hope this all becomes a distant memory.