Fortunate timing, I accidentally drained the battery in one of our vehicles (a 2.0 L gas engine) the day before this arrived. Honestly I'm glad I did because I got to confirm that I knew how to use it and that mine was a good unit. I'm sure some of the bad reviews are from bad units (so fair enough), but I suspect many are from people that haven't taken the time to understand how to use the it. My battery was too low for the auto-sensing feature to work (car battery completely dead) so I had to use override. It didn't work at first because I (my fault) hadn't made a clean enough connection to the battery terminals (there is a reason the unit doesn't allow extension to body panels for the negative/floating ground like standard jumper cables). When I did get a clean connection to the terminals, it worked like a dream. All of this is documented in the manual (which is translated into more languages than I knew existed). So... Read the manual! Great product and I highly recommend.