It probably better to leave the small blue battery to the left plugged in for the Bios Chip. Just lift the batter out of its holder and move it out of the way as the cover is moved. If unplugged the computed will ask you to run setup when you start the computer.
Need to add a caution when rotating the cover to be careful with the hinge post on the right side. you can snag the GPU heat pipe as you rotate the cover. So watch the maneuver.