AP or Android Pay uses what's called NFC or Near Field Communications. Basically a communications network is formed between the devices when they are close and they can exchange data securely. The device need to be close but they do NOT need to touch. I'll use my Daydream VR headset as an example it also uses NFC for it's remote control and the remote is sometimes about 1 foot away sometimes maybe a bit more and it still works fine. I highly doubt the extra distance that the battery mod forces on you will matter. NOW that fact that it's a battery may make a difference but again I doubt it as the device also has a similar battery in it which doesn't seem to affect NFC. NOT knowing for sure, BUT I think I can fairly confidently say you should be fine.