I just bought this unit. First off I would like to point out. Most of the users that are not satisfied with this unit should read the instructions. And you can spend a lot of money on a name brand battery booster. Most of them do not last more than a couple of years (Keep it charged and you might get 3 years). You are talking about a rechargeable battery. I am in the industry and you can pay 150 for a unit it will last the same amount of time.
This unit has a internal charger and it is a float charger, that means you can leave this unit plugged up all the time. Matter of fact if you read the instructions. It tells you to leave it plugged up all the time to keep the charge going. This will make your unit last much longer also. Never never let a rechargeable battery go dead and stay dead for a period of time. This will definitely kill the battery and it will not take a charge. It's the same method with your rechargeable batteries on a drill whether they are lithium or whatever. Never never let a battery go completely dead for a period of time.
For 69.00 dollars at Costco you can't beat that deal (this is for home use and recreational not for being used in a shop). I have purchased Schumacher battery boosters before and they last just as long a couple of years and they cost much more. If you want one for a shop, try the Solar E2500 or E5000, they cost about 130.00 to 180.00 and they will only last maybe a couple of years on the rechargeable battery, but are heavy duty for a shop or even a Clore battery booster for about 300.00 plus and that will last you about 3 to 4 years.
I have not tried the jumper yet. But like any jumper, most will not start a totally dead or defective battery. Some jumpers need some voltage in a battery to get it to activate, not sure about this one yet. But it has saved me when my cell phone died a couple of times, me being a knucklehead and forgetting to charge my phone. I have not used the compressor on car tires yet, but I have used it on my grandkids basketball and it was fast. Also the light is bright, would like for it to have been more flexible but, Its ok. Overall, excellent Unit so far for what I paid for and the purpose of this unit.