I'm guessing you can open the driver door with your key? If that is true then access to the OBD II data port is under the dash and diagnostic codes should be available.
Here is a link that others have used to open the rear hatch, just click: open hatch
Give us more details on the battery change with the FOB. Are these FOBs original? Can you see a red light flash when looking at the front side of the key ( there is a red lens) when you press the open button. There is a RF chip in the FOB which must be the original that came with the car in order for the doors/hatch to lock/unlock.