Usually this happends because of when water is added to the battery. I usually recommend having only 1 person in charge of watering the batteries. Once a week is usually works in most environments. Monday mornings at the beginning of the shift after the lift has equalized over the weekend and cooled down. Unless your battery is bone dry you don't want to add water right before charging. If you have just 1 person in charge of watering all the batteries should help with over watering. Even with a watering string you can over water.