Successful jumpstart straight out of the box, on a battery dead for weeks. I wish I had known about these devices, I wouldn't have bother my neighbour on the first jump. Then after a couple of weeks, I learned that my battery had died again, due to lights left on. After reading reviews from low-star rated people, I learned that they were getting the wrong Ampere, example, for SUV models get at least 1000Amp. I did a lot of research and decided to get this brand despite any negative feedback. It was delivered next day, and already had 75% charge; so I made the attempt to jumpstart even though my battery was depleted over a couple of weeks - the jumper successfully started my car at fist try THANKS TO BOOST button on the side of the adapter. I also love the cigarette lighter outlet feature, because I have a mobile power-wash that needs that power source connection, and which I plan to use once every few of months or so to clean my deck. I also love singing in my car, I need to keep my phone charged while I play my music. I LOVE THIS JUMPER POWER BANK.