Since I was out in the garage. I also leave a yellow towel on the driver's side door handle so I don't jump in and try to drive off without unhooking the battery tender. For the battery, I use Interstate. First one had a faulty cell after a few months, no question exchange at Interstate. From now on though, I'll get them from Costco as they are very cheap there. An Interstate for my GX460 was only $80 at Costco.

 

Long story short most folks dwell upon voltage, just as they do HP and not so much torque. They don't measure CCA, which is needed to turn over the engine. So the battery tender keeps the battery at the proper voltage. They never said your car would start as a result or that it would not start without.

 

We have two Costco batteries now, I like them too. Quite inexpensive. Someone here says he just gets a new one every 2 years from Costco for free?

Too bad they don't have the proper size for the BMW, I'd trust it. I even see that my wife's casing changed and now they have handles on it, before, they didn't. Vent tubes in the proper place, too, as hers is inside the vehicle.