The overall verdict is this is a poor quality jump starter which has an unreliable charger and a battery that will die if you don't look after it. However, I found one fair report on Amazon amongst many bad ones:
"The compressor on this unit, like so many others this small, is really only made for pumping up toys or bicycle tires. So don't buy this unit for that purpose. Go to a gas station with quarters and use their air vender.
If, like me, you bought a used unit, you will need to get both the manual and the charger. Do a search on servicenet dewalt to find the owners manual. The manual is a download pdf. Charger model number is 514005-42.
Hope this helps. It's really a neat little device to have around. I especially like the built-in LED flashlight.
You really NEED to read the manual all the way through. The special sealed type battery requires charging at least every 60 days or it WILL go bad quickly."
The Manual is here: http://documents2.dewalt.com/documents/English/Instruction%20Manual/Vector/VEC010BD.pdf
Because I'm an engineer I know I could easily replace the 12v lead-acid battery charger, open the box and replace the battery with another 12v say 200 Amp cranking (short circuit effectively) battery but I would tend to spend a bit more on a gel battery of similar spec 'cos it basically is the only sort that should be used for deep cycle discharge with such a small volume battery. Good luck.