Is there a way to use a key to open the rear hatch door, car battery dead 2009 equinox

Yes, you should be able to use the key to unlock the rear hatch of your 2009 Equinox even if the car battery is dead. The lock cylinder for the rear hatch is likely located on the outside of the hatch itself, or it may be located on the door handle. To unlock the hatch with the key, insert the key into the lock cylinder and turn it clockwise. If the key won't turn or the hatch won't open, you may need to wiggle the key or apply more pressure to unlock the hatch. If the key won't go into the lock cylinder at all, it is possible that the lock is frozen or damaged and will need to be repaired or replaced. You may also be able to use the manual release for the rear hatch, which is usually located inside the vehicle, near the driver's side door or on the underside of the dashboard.