Tests of the batteries after being recharged by two separate types of chargers,
for more than a day each:
These batteries are relatively new, however in mid-January 2019 my van's original engine seized/died,
and it sat outside (far northern WI) for two months.
During that period, the area was hit hard by a "Polar Vortex",
with temperatures often below -20F,
so the extreme cold combined with snow on top of the solar panels,
likely damaged the batteries.
My friend recommended replacing them.
It was early Spring, and solar harvest would improve dramatically for several months,
so I asked his advice on waiting a season (until late fall or early winter),
so I could get some final use out of the old ones, and save some money.
He was very supportive of my idea.
He walked me thru reconnecting them, so I'd be ready.
It's eleven months later, and while they were definitely sluggish (mostly in "bulk" rarely reaching "float") during the period around the Winter Solstice (about two weeks before & two weeks after), they've otherwise been chugging along fine. :)
During May 2020, I spent a couple of weeks at a forest site,
where the leaves "came out" and gradually diminished solar harvest.
This caused another "zombie" period
where the batteries dropped to zero percent for a few nights yet revived each day.
I have been particularly careful about not overloading them, which is crucial.
The key is do all optional charging during peek sunshine hours, so I carefully monitor the weather and plan those loads, particularly my crockpot. :)
If I had a fridge, I would probably have had to replace the batteries, to support that all day load.
Jim, they're dead... yet, they're still useable. :)
My Plan is to continue to use them, carefully, and only replace them after there is a prolonged period of problems.