Always add water AFTER charging, unless.....
the electrolyte is not or is just barely covering the plates.The level will go up when charged, and I suspect that this is your problem. Additionally, if the electrolyte is actually over-flowing, I think you have WAY over-filled the cells also. You said that you didn't over-fill, and given that as fact, I am at a loss to explain the spillage.Adding a large quantity of water to battery cells can easily dilute the acid below the "normal" range and render the battery un-usable. I would remove some of the electrolyte with a syringe to restore the normal level and then measure the specific gravity with a quality hydrometer. If after fully charged, the SG is below 1.260, then either the battery is at end-of-life or it has been over-watered.I have had some success adding concentrated sulfuric acid to an over-watered battery and have been able to get another year or two of service out of it. However, obtaining concentrated sulfuric is not easy (I got mine from a college chem lab) and you must be very careful in handling.In answer to your last three questions- I don't think the charger is at fault, it is definitely NOT normal, and yes, you may be out two batteries.