beemerphile1 wrote:
I use one of these;

Sometime the batteries are crammed into spaces that style won't get to all the cells. Tried on on our new coach, not the solution. Even other methods are hard as you can't see how full it is and you over fill it.
We've use the flow rite product. This is our second coach and have just installed again on this one. Last coach was 5 years without a battery issues using the system.
Other than that maintanance free are the way to go, but costly.
https://www.flow-rite.com/battery-care/brands/pro-fill-rv/