The keypads have been a problem. I believe that PT has discontinued adding them to the tt's, which is too bad because I really like this feature.
They did have to replace my keypad and everything inside the door, but the keypad has worked great since then.
As I undersxtand it, you have to gently pry the keypad off the tt. I believe there are 6 or 8 tiny screws you have to remove from the backside to replace the batteries. I think you'll need to get something like 3M double sided tape to put it back on.
Just to note, if your keypad lights up then it shouldn't be a battery problem.
Since this will be covered by your warranty I suggest you take it to your dealer to fix as I did.
One thing to check is the contact points at the bottom, inside of the door jam. Make sure these are clean. Also check your breakers. I have one labeld "Entry Door".
In case you didn't receive any, here's the keypad instructions.
Hope this helps.
Let us know how things turn out.