Honestly, I was skeptical about this unit but it proved itself the other morning, I actually left my keys in my truck with the ignition turned forward on a -20 F Rocky mountain night. The next morning I found my battery as dead as it could possibly be, I thought there is no way this unit is going to start my truck, it was still -5 at 7am and I was without hope. I started to call my neighbor then thought well I should at least try it. So after hooking it up like I thought it should be hooked then only to realize I wasn't doing it right I finally read the instructions, (read the instructions) The system gives you a 15 second blast window to turn your vehicle over, It took 3 tries but then the truck to my astonishment fired up and rip roared to life. This is not a charger or power transfer system, it is a booster and boost it does, I was thoroughly impressed with it, Even after my misdirected hookups and the 3 turns it took to start it there was still 97% power left on the system, Plus the system sat in my truck for month in the dead of winter and still had a 100% charge on it. It comes in a nice compact case and a built in flashlight. I am satisfied.