How do you change the battery & program a Toyota Corolla key fob?

Replacing the battery in a Toyota Corolla key doesn't require re-programming. You simply use a good quality flat-head screwdriver to carefully pry the two halves of the key apart. Once you have them separated carefully pry out the middle case, then carefully pry it apart. The small round battery is inside and can be replaced with any CR2016 button cell battery, remembering to leave the positive side up. The key can then be reassembled in the reverse of these instructions.