I have 2 - one from a few years ago that I keep in the car, and one from the recent TSV, in the house. Luckily my area very rarely loses power, but just in case ...
Last winter - same story - my dad's car wouldn't start. My BIL was going to get his cables and I said "Oh wait ... " He also didn't believe it would work. He was shocked when dad's car started so easily.
And same story with my sister. Her car wouldn't start in our driveway. While she was on the phone talking to her husband, I took the cables out and started her car.
Love my Halo!