Remove the 3mm screws using a #2.0 Hex screwdriver. There are 4 of these screws (2 on each side) that connect the motherboard to the battery unit.

When the screws are removed, use an iFixit opening tool to remove the motherboard from the two clamps securing it to the battery pack.

Beware! The motherboard is not fully disconnected from the battery even when removed from the clamps.