The solar guy is completely correct.........10 years ago.
Back in the day, a charger put XX power to the battery, even the automatic ones put XX amp rate until the battery quit absorbing power, the voltage would go up, the charger would quit.
Now, most any charger/converter is a smart or multi stage through the advent of processor technology. A 70 amp rate might start out at 70 amps, but progresses through 40, then 20, then 10, then float which is a very slow rate. The numbers are arbitrary, but show the example.
That means that the batteries don't endure as much as they charge, they don't get as hot, meaning they don't boil off water like they used to.
So, we lose very little water. I've had four 6V batteries in mine for four months now, cycled them from 12.3V to fully charged for over two weeks straight during that time, they're still full.
If you're charging rate meets your needs, then don't worry about it. If you're losing very little water I'd consider that a good thing, means you're not working them too hard.
Now-2014 Sierra 346RETS 5er BUB
Then-2002 Keystone Springdale 286RLDS TT
Nights camped in 2014-28, 2015-127, 2016-10