These "cheap jump starters" are little more than a Lead/Acid battery much like what is in your car. If they sit too long on the shelf of your local department store, without having a charge maintained, the cells in the battery will eventually collapse rendering them next to useless without quite a bit of work trickle charging them back to life. As the proud owner of several of these useless boat anchors I can advise you to save your money and just buy a really good vehicle battery (Interstate) that will be there when you need it, instead of wasting money on Wallymart specials that last 2 maybe 3 years. I have learned..... ;-) Take it back and get your money.