Volkswagen cars sold since 1998 have come equipped with a "flip key" or a "switch blade" key. Because of the unique construction, it may appear intimidating to replace the battery; however, it's simple and doesn't require you to visit the dealership service department. You will need the correct replacement battery. Bring your old battery to the electronics store or contact your dealer to determine the correct battery number for your Volkswagen.
Flip the key blade to the "Open" position and place it on its side.
Insert the flathead screwdriver into the notch (in the slot your key rests in when it's in the "closed" position). Pry open the key, separating the top half (key) from the bottom half (remote).
Pry apart the remote transmitter using your hands. Set the side containing the circuit aside.
Remove the old battery (use the screwdriver to pry it out from the side) from the transmitter. Insert the new battery with the "+" symbol facing down. Push the battery down to secure it.
Snap the remote transmitter halves back together. Position the key half on top of the transmitter and push it down to lock it.
This tutorial also applies to Audi vehicles; they use the same key as Volkswagen.