Unscrew the 5 P1 Philips screws (2 under the rubbers). You can esaily follow: HP official video to Remove the Base Enclosure

Once you pull up the sides of the cover (e.g. with a pick). You will feel it is still attached in the middle. You can squeeze your hand under the enclosure and push from the middle to liberate a clip in the middle of the enclosure. Pulling directly from the sides feels like the cover will break.

If you are not sure of the model of the computer/battery. you can do this step to check the battery model before buying it and then close it again doing the inverse.