IMO you have to wait a few days to get the true resting voltage that goes with their SOC or condition. Note that a "full" but sulfated battery shows figures somewhat like the SOC tables for how much it has lost capacity. EG a full batt that has lost 20% might show 12.55ish resting when full as it can get, with SG maybe 1.260 approx.
I have some notes from a few years back when monitoring "resting" voltages after getting the batts to as full as they would get hitting 16v. These were (two older , one newer) 27DCs but got similar results with 6s ISTR. Three batts separated, each acts a little differently.
The idea is to figure out when surface charge goes away and you are at actual resting before the "self-discharge" starts
Next day not 24hrs yet, all were still in the low 13s so starting day after that (Day, batt 1, batt 2, batt 3)
1- 12.86, 12.87, 12.89
2- 12.83, 12.82, 12.88
3- 12.80, 12.78, 12.86
4- 12.79, 12.76, 12.85
5- 12.78, 12.74, 12.85
6- 12.78, 12.74, 12.84
7- 12.78, 12.74, 12.84
8- 12.77, 12.73, 12.83
9- 12.77, 12.73, 12.83
14-12.76, 12.72, 12.82
20-12.74, 12.71, 12.80
With two beat- up 12v true deep cycle Trojan T-1275s charged to 14.94 together, then separated:
one hour later- 13.43, 13.40
next day - 12.93, 12.90
2- 12.80, 12.76
3- 12.73, 12.68
4- 12.66, 12.61
5- 12.63, 12.59
6- 12.62, 12.58
A year later, the two T-1275s are still different where I can identify which is still the better one. I use them in parallel and separate them to float when not camping.
So it appears to take a few days before the voltages stall out to what may be the "resting voltage" and then slowly fall from there.
Self discharge is less if the battery tops are clean. If left linked with another battery then there can be action between the two that affects the voltages.
