A spare battery for the key fob can be found in the dashboard compartment aka glove compartment of your Spaceship.
Open the battery compartment of the key fob. To open the key fob, find the small grey button on the side with a picture of a key. Press this button. While pressing, pull the top part where the key ring is attached. A small key will come out. Now, find the slot where the key came out. Put the small key into this slot and turn it to the right (clockwise). This will open the plastic cover of the key fob, and you can now change the battery.
Remove the old battery and replace it with the spare battery.
Close the key fob. First, take the plastic cover and place it back over the key fob. Make sure it fits properly. Next, take the small key and insert it into the same slot. Turn the key to the left (counterclockwise) until the cover clicks back into place. Finally, press the small grey button on the side of the key fob and push the key back into its original position. The key ring should be attached at the top again. Now the key fob is closed and ready to use.