I noticed a 1/4 inch circular wear mark on my St2 battery. Found the 6 small Allen head screws in battery compartment holding controller , had become loose . I use a strap on the battery door , or I think controller would have just been hanging. Some screws had rust on the threads. I replaced with stainless steel screws and blue-loctite. Pretty detailed process to change. If assistance is needed I will advise, The screws are different length , so watch out for that.