VERY IMPORTANT:

The battery connection on the motherboard has a small metal sheath that slides back, which will allow you to remove the connector without breaking anything. The metal piece slides back and forth to secure the battery connector, so to remove and insert the new battery, the metal sliding piece has to be slid back, then you can gently remove the connector without breaking the plastic part attached to the motherboard. Mine didn't move that much, maybe a millimeter or so, just enough to give clearance to remove the connector from the interlocked plastic parts.