Yes batteries can die randomly. Batteries can also have a residual charge strong enough to turn on the headlights but not start the car. Batteries can also die out of nowhere in cold weather regardless if they are inside or not unless of course it is a heated garage. Jumping the car will allow the generator/altenator to recharge the battery. But you are right there may still be other problems. Why are you looking for a ground exactly? At rate any bolt screwed into the frame of the car will so.