Acer Altos R720 Series - Manual (Page 106)

3 System upgrade 96
6 Engage the hooks on the back of the battery into the matching
chassis tabs, then slide it toward the power supply to lock into
place.
7 Connect the power cable between the BBU and the mid-plane
board.
8 Replace the air baffles and CPU air duct.
9 Observe the post-installation instructions described on page 36.