I have to keep a eye on the water level in the battery like 2 or 3 weeks. Then about 3 months or so i have to replace the battery. If i run the machine for like 2 hrs or more at a time i can see the water being pushed out of the over flow on the battery. And can smell it, but on most jobs when the machine is only run 30 to 50 mins its ok. Its a 18 HP B&S I just put another battery in today that is the 3rd one this year.