when should a powermax pm4b drop into float mode

So how often did you have to add water? The voltages aren't high. I have new batts and have done a dozen cycles on them at 15.5 volts and not needed any water. They gas a little on each charge too. i can smell them but the temp is low. I checked on the last charge and the temp on the battery case went up about 8 degrees to 83