http://www.ebay.com/itm/261201404201

I popped off the rear cover to reveal 2 screws. I removed both screws.

Remove board as shown.

Start removing old buttons. Use caution and work slowly. 

I broke a few tabs but all is good. Again use caution.

I cut off the fake led light as my key had a real one.

I needed to cut a corner off the lock button to clear the chip.

The chip had some adhesive holding it down preventing it from rattling. I used a dab of shoe goo to hold it in place.

Put it all back together with a new battery and all it good.

If replacing battery, you have 30 seconds to get the new battery in once the old is out. It took me about 3 seconds so it should not be a problem. If battery is out for longer you will have to re-initialize the key.