I had an S1 for 3 months. Then one morning my car wouldn't start. The battery was dead and could not be re-vived. I got a new battery and did some testing. With the S1 I was seeing 15.2 volts (14.9/15.0 at the battery). Upon removing the voltage booster, I was seeing 14.2 volts. All has been fine for over a year, and I have an S1 sitting in my parts pile.