rollyfingaz, as I understand it, the NFC chip installed in your galaxy nexus is embedded within the phone. I came across this post searching for a similar answer after speaking to a Samsung representative regarding my Samsung galaxy s ii skyrocket. The answer I received was that the NFC chip is embedded in the phone and no special battery is required to power it.
I would add, though, that when I asked if the NFC functionality would work with a third party battery, the Samsung rep did not know the answer.