Pontiac Problems? Ask a Mechanic for Answers ASAP
I'd start by charging the battery you should be able to do this via the cigarette lighter / accessory socket. You'll need the appropriate attachment for your charger but car accessory shops sell these- Alternatively if you can't get into the car/ boot the other way to do this is jack the car up so you can get under the front.
Locate the starter motor and the large power cable that runs to it - connect the positive battery charger lead to this terminal
then connect the charger negative lead to the metal of the engine block
This should complete the charging circuit and get some power into the battery allowing you into the car
OK there should be a key hole in the rear hatch still?
so you can use your mechanical key to turn the latch and pop the hatch open
and I think there should also be an emergency release inside the trunk under the trim panel at the side
if you can't find the emergency release in the side panel then it may be on the trunk lid / hatch attached directly to the lock
I'll opt out to open this up to others