A few things to consider..
Temperature will affect how long you need to wait for the surface charge to dissipate. At 80F, 24 hours should be sufficient but some batteries such as GEL and AGM
can take longer. If the battery was just recently equalized 24 hours will not bring you back to rested voltage. In colder temps the surface charge can hang on for days and weeks even in flooded batteries. Many installed charging systems chronically under charge batteries due to short absorption times due to "egg timer" type charger algorithms. This means your time on float,
to get to full, takes significantly longer.
I have a number of AGM
& flooded batteries that have been off charge now for at least 5 days to 7 weeks that I just measured at 12.73V to 13.03V. Shop temp has been running about 74F to 78F for the last month.
Odyssey PC-2150 = 12.94V - Off charge for approx 7 weeks
Lifeline G-31 = 12.92 - Off charge for approx 5 weeks
Northstar Slimline = 12.98V - Off charge for approx 8 days
Deka GEL = 13.03V - Off charge for 4 days
Full River DC335 = 12.99V - Off charge approx 5 days
Firefly G-31 = 12.93V - Off charge approx 3 weeks
Deka G-31 = 12.78V - Off charge approx 7 weeks
US Battery G-31 - 12.74V - Off charge approx 10 days
Trojan SCS-225 - 12.73V - Off charge approx 7 days
Measured with a NIST Calibrated Fluke 179
If you are setting the bar at 12.6 - 12.65 your batteries are simply not getting fully charged or they are very aged.. I see very few batteries run through my shop that have resting voltages below 12.70V. When every 0.1V is roughly = to 10% of capacity......
Here is an interesting image to ponder if you think using a generic scale of 12.6V - 12.65V is a full
battery. The only guide
for open circuit voltage is the one your battery maker supplies or suggests for that battery.
This is a 110Ah AGM battery 1:23 minutes into a 20 hour capacity test. As can be seen we have removed 7.677 Ah's and the loaded voltage
is still 12.766V. This is the loaded terminal voltage
after 1:23 minutes at the 20 hour discharge rate of 5.5A..... How much capacity would we be leaving on the table to consider this battery full
at a 12.6V - 12.65V resting voltage
....??? How much chronic undercharging would be occurring & sulfation would occur if we deemed 12.6V - 12.65V for this battery as a full battery
Bottom line is don't let your batteries drop below 12.1V - 12.2V under your normal house loads
and you'll be doing okay. Trying to get an accurate resting open circuit voltage, while cruising, is tough.