We are talking about the auto-fill systems, like this one:
https://www.flow-rite.com/battery-watering/pro-fill
They are supposed to be self contained and you are not supposed to ever have to take the caps off, etc.
Based on the three fleets I have serviced that had them, no one other than me seems to care if they are working or not. They just hook them up and don't pay any attention to leaks or overfills. I have been the only one to call it to the attention of the dealers or manufacturer.
I know how important it is because I saw E Z Go stonewall a system that didn't work, and wind up replacing 117 batteries before they gave up and replaced the fleet.