The only matching part number that could be found so far, was that of an 1150 mAh battery. It's always possible that the part number was reused for a higher capacity one, we just don't know yet.
Size could be a factor.
Another possibility is that there will be a higher capacity battery (of the same size) available later for an upgrade price. This would explain the lack of soldered wires, and the external screws.
An extended battery option would sell like hotcakes. And Apple would look like a hero while raking in the cash.