How do I open the trunk if the battery is dead and key is stuck in the slot
My car has 100000 miles.
My car has an automatic transmission.
If you can get into the car, you are halfway there. You can temporarily power up the system through the cigarette lighter’s electrical connector. There are devices available that can plug into the power socket of your car and energize the system enough to operate small things like door and trunk locks.
They won’t start your car but will make it possible for you to access the trunk to replace the battery. You can find them at auto parts stores.
I recommend having a certified technician, such as one from YourMechanic, come to your home and replace the battery and talk to you about getting that key out of the switch.