Removal steps of bottom cover - Please perform the following steps as shown in the pictures below.
Slide the bottom cover latch to the unlocked position . Hold the latch in the unlocked position, and then remove the bottom cover .
When installing: Slide the bottom cover latch to the unlocked position. While holding the bottom cover latch in the unlocked position, attach the bottom cover , and pivot it downwards until it is firmly attached . Release the bottom cover latch to secure the bottom cover.
The tabs  on the bottom cover will cause a safety risk if they puncture the battery. To prevent damage to the li-polymer battery and to avoid the risk of high heat and fire, ensure that the tabs on the detachable cover are carefully aligned with the chassis prior to re-attaching.