Most of our walk-behind pallet jacks use valve regulated 6V batteries in series to 24v total. A float charge is for standby use. That voltage prevents excessive water loss. Our pallet jacks charge to 28.8 in cyclic use, hard up and hard down. That keeps them equalized, but they don't last very long like that. They dry out after 2 years or so.
If you want to get the maximum life out of your batteries, they need to be charged individually to 14.2v
That won't ionize water in the battery much.
If you run them way down, don't let them sit that way. That leads to hard sulfation. Below 12.4v is where hard sulfation begins, don't let them sit for hours each day at that level and you should be fine.
A parallel/series setup makes it hard to equalize, unless you have a separate charger for each battery.