O.K. , I understand your question .
I'm no battery guru but this is what I remember and the only thing I can think of trying.
When you check the batteries do you use a hydrometer to actually see if the battery is charged or discharged ?
They say do not water any discharged battery. The way to water a battery is to fully charge it, check the level of the electrolyte then add water to bring the electrolyte up to level ,otherwise you are adding too much water to them.
If you are not doing it that way, you might be damaging or have damaged the two batteries on that one side.
If you swap the batteries will the other two batteries now need water ?
OR do the same two batteries ( which are now on the other side) still in need of water. If so, I suspect those two might be damaged.
Swap the location and see what happens .
bob
