Originally Posted by Qsilver7

Since you mention you tried jump starting the car...you can hook up jumper cables (again) to the positive & negative terminals in the engine bay (or you can use a battery charger or tender)...this will give the car enough power to unlock the tailgate using the interior tailgate release button...or your remote...or the release pad on the tailgate handle. Just remember to NOT shut the trunk (all the way) if you don't have an auxiliary power source to power the tailgate when you need to reopen it.

Hopefully you know how to use the mechanism that facilitates removing the spare so that you can access the battery compartment. If you don't...there used to be a really good video on Youtube that shows how to use the built-in straps & handle...and the brace that holds the tail gate in place.