Mismatched marine batteries.
Without temperature compensated floating of fully charged batteries, I'd disconnect them, put them somewhere cool, and top charge them every so often.
as opposed to letting them bake outdoors being fed a constant 13.2v, or whatever the converter or solar tries to hold irregardless of battery temperature.
but they are mismatched marine batteries a few years old.
They likely have quite high self discharge with one worse than the other.
Might not be worth the effort or trying to extend their feeble lifespans.
Just get em full and try to keep them there and nearly full.
If you can't bother with dipping a hydrometer to ensure they are full when the charging source proudly claims so, then fretting over their longevity is obviously not a priority either.
Those of us who have decided to go beyond what a green light tells us, have seen that flooded 12v marine jars require significant coaxing with extended periods at high absorption voltages to achieve 'full' charge, and full is in quotes as even extended absorption durations maximum specif gravity only seems to be achieveable with times spent in the 15.5+v = range, which is an EQ charge.
How many converters actually do 15.5+ volts? One?
The converter companies calling their 14.4v every 21 hours from float stage, an equalization charge, is modern marketing at its most contemptible.
Does destratification mean equalization, as it applies to stages of battery charging. NFW.
Get them full, keep them cool.
