Smart Key Confusion

Hello all!
I have a 2008 Package 5 or 6 car, not sure but it is loaded. Recently I've been having trouble with my smart key system. It hasn't left me stranded but often with the vehicle running it will think that the key is not inside the vehicle even though the key is in my cup holder. Also recently when attempting to lock the vehicle using the button on the door, nothing will happen, no lock no beep, on either door. Then it will work as usual. I replaced the fob battery (dealer does it for free) and upon examining my fob it seems to be making a rattling noise on the inside that my spare does not. I have a brand new programmed spare key I've never used so I will try using that key for now and see if the issues continue. Didn't know if anyone on the form had any insight into this problem.

Thank you and I appreciate any and all help!

 

Thank you for the reply, I have not taken apart the key yet, but for some reason I suspect that the broken piece in the key may be part of the antenna for the key.

 

12v health is a okay, just had my service done at my dealer and the battery was tested and passed. I also have not had any symptoms of 12v battery failure. Thank you for the reply

 

I checked my key and removed the battery door to make sure of that, they did put the screws back properly. As for weather they replaced the battery or not, the battery looked new and I did not watch them do it myself but I'm pretty trusting in my dealership.