Well that will be the case because if you have a bank of series connected batteries each battery will discharge into the other and eventually they will equalise and all will read the same.
You probably have 6 parallel banks of 2 x 12v batteries in series ? (standard Amel setup)
However if you charge the whole system and then immediately disconnect each battery you may well find that they are not all the same.
We have 6v batteries..4 in series and three of those banks in parallel.
We had serious issues with battery failures 12 months after the new batteries were installed, probably caused by the slightly different internal resistance of each battery in the series chain. Some batteries were being more charged than others.
We replaced the failing batteries (under warranty..hard to believe, but it happened) and installed battery balancers on each bank....they make sure that each battery in the series chain receives the same voltage
Since then ... 2 years..we have had no battery failures and our 660Ah house bank is still 100% capacity.
We monitor and log voltages vs capacity on the Link 10 compared to actual discharge...we never go below 80% and so far all the measured parameters are consistent.
BTW our batteries are AGM .. so limited gassing issues and almost no possibility of explosions !
600W of solar with a Victron MPPT controller
A D400 wind generator that seems useful in gale force winds, but o'wise...PITW
100A Victron charger
30A Pro Mariner charger
175A Leece Neville engine alternator coupled to a Next Step II regulator
AND they are all set for the same (batt Manfr rec.) voltages, absorption times etc
And so far ...it all seems to work !
Hope that helps
Port Havannah, Vanuatu