OK, I have to throw this in about jump starting vehicles.
First you need a good quality jumper cable set. Most of the sets you purchase are just 10 gauge wire with a heavy outer coating. These cables wont handle much amperage. If you are trying to jump start a vehicle with these you will need to let the vehicle run for awhile to put some sort of charge in the dead battery. The larger the load the more amps it is going to take to turn over the starter.
When purchasing a set of jumper cables pull back the insulated rubber grip and look at the wire, if it is the size of a soda straw it is about 10 gauge, ok for light stuff but on a totally dead battery you will still have to let the running vehicle charge the dead battery some.