Originally Posted by Lee
I typically turn the batteries off when park for an extended period of time, the charger tends to "boil" the batteries and lead to a need for refilling the water in them about every three to six months, NEVER had an issue doing this.
If your batteries are boiling plugged in your converter is faulty or the batteries. Leaving the unit plugged in w/ batteries connected is the best way to store & maintain the batteries.
The converter should only provide the charging required by the charge of the battery, either full charge, to trickle, to float, but yes all flooded lead acid batteries will require topping off w/ distilled water periodically, not necessarily due to boiling but just due to charge discharge cycles.