Thin plastic film on replacement battery - a question.

I bought a replacement battery from iFixit for my early 2014 Macbook Air. The guide on iFixit website says to leave the "thin plastic film" that comes on the battery on it. But, the picture on the iFixit website looks different from the thin plastic film on the replacement battery I received. The Apple OEM battery I removed did not have any such film on the battery. So, how do I know if I actually should, or shouldn't, keep this thin plastic film on the battery after the install?