You need a data connection to get your credentials into the NFC chip, and get data from the chip.
If there are no pins allocated for data, then it can't work. I'm not discounting that some mfrs have the forsight to include "reserved for future use" contacts that they could define for it. Or that some phone batteries may even have the signal paths required. Apparently, some older blackberries had extra connections and were able to be retrofitted because of this (through data port, not battery).
That's if NFC is even in the battery, which I'm not convinced it is. While the battery may be marked with it, it could just be the only location for marking. Not uncommon in tight spaces to mark where ever you can. The Nexus S has it's NFC chip in the rear door (so I read).
Now, there are some SD cards that are supposed to be marketed soon that will have NFC.
However, I thought you might get a laugh at how the iPhone guys do it.
Add NFC payment capability to your iPhone 4 | TiPb