Will the Phantom 4 pro batteries work in the Phantom 4?

Yes, but currently it would require you to refresh the craft's firmware level as you move the battery back-and-forth. Alignment of the battery firmware (contained within each craft's firmware) should occur with the next P4 firmware release. As it stands you will receive and 'Incompatible firmware' message when you power everything up - it's referring to the battery's.

Punchbuggy hit the nail on the head.

Thanks for the replies.  I appreciate the help