This happened years ago too.
When I place my MBP over a table it's not stable because I can see a weird curvature on its bottom caused by the swollen battery. I took it out and from one side it's ok, but the other seems it "grew", so one side is wider than the other.
I've been with this battery at least 5-6 years, so I take it it's simply time to get a new one?
