Does anyone know how to replace a battery on key fob on 2007 TL type S?

I removed the little screw and took apart the two halfs of the key fob but the internal piece that has the 3 buttons appears to be sealed. any idea how the get to the battery?

Thanks,

h.

 

I figured it out.

 

Any trick to it? I need to replace mine, but haven't bothered actually looking at it yet, just been using the other key.

 

How do you know when it needs to be replaced? (besides when it stops working loll)