What to repair with swollen battery?

Hello all

I found an old Macbook Air of my girlfriend which she doesn’t need anymore. She stopped using it because of the battery that was swollen (see attached pics). I know that when you take it to the Apple Store, they will also replace the top case.

I like projects like these (trying to make it good again). I know it’s an old thing and is not really worth my time, but like I said, I like it. Am I okay with only replacing the battery or do I need to replace more?

Thank you!

Korneel