Important suggested edit to these instructions - make sure to pry off clips/ridges from BOTH sides before attempting removal of the cover.
I interpreted these instructions as saying you only needed to pry clips from one side - then peel off cover. Doing this broke a clip from the other side. Bummer. I'd like others to avoid that.
Similar to the other comment - I agree - this step was incredibly difficult. It took me about an hour of gentle prying, wiggling, and forceful pulling to get it out. In the end, VERY cautiously using a pair of broad nosed pliers was what allowed me to pull out it.
Bloating I'm sure does play a role - but I think the main factor is the foam wrapper around the stock battery. It makes it stick to the battery channel.
You have to be extremely cautious when doing this step, as you don't want to rupture the battery but need to apply a considerable amount of force to get it out with not much leverage for your hands.
The end cap has some kind of adhesive on it. I’m a strong guy and couldn't pull it off. Sliding a plastic pry tool around the edge helped break the adhesive and make it removable.