Toad, it would not surprise me to hear that the battery is going south on you. My little BMW caused me a bit of heartburn in the first 6 months I had her, suddenly dead as a doornail a few times. The dealer did a load check per BMW USA and it passed. Still left me on the side of the road again. Frustrated, I just bought a new battery from Batteries Plus and everything has been golden for the past 18 months. BMW seems to ship the 650 with a crappy battery. As for getting another battery from Wallyworld, a battery shop would be a better bet. All you need is the exterior dimensions and orientation of the battery posts, then find what fits (maintenance free). There are three Batteries Plus locations in Tuscon. I just checked the BP site and they list a battery for the '09~'11 Stelvio, don't know if it's the same as on our '12 but I suspect it is. For grins I'd have BP do a load check before you write the check, seeing it fail would make me feel better about thinking that I have solved the problem rather than just throwing money at parts and not actually fixing an underlying problem.
Growing old ain't for sissies!