First of all, the batter is a lithium flat cell...available at any Radio Shack.

1. First, use a flathead screw driver to pry into the little rectangular access hole on the VW emblem side. Pry the plastic piece in the up and "pry apart" motion.

2. If you pry properly, the keyfab should separate like the picture.

3. Here is another view from the other side.

4. Separate the keyfab into two pieces.

5. Just by using your fingers, pry open the cover on the transmitter side. Be gentle. You don't want the batteries to fly out.

6. Gently, flip the cover over. There are two type CR1620 lithium cells snapped in on the cover. Remove, replace, and re-assemble in the reverse order. The keychain ring will probably fall off at this point. Put it back before assembly. Don't touch any of the electronics because of ESD danger. You may fry the chips.