Noticed last week the battery was swollen on my old 2015 MacBook Pro. The case was bulging and the feet no longer touched the desk, so it rocked as you typed.
Checked with Apple, and mine was not one of the ones covered by the battery replacement programme 
This machine has been used loads, so guess I’ve had my money’s worth.
So my options were pay around £110 for a third-party battery and fit myself (plus deal with disposing of a leaking Li-ion battery.) Or Apple offer a £199 battery swap, that they claim is the parts cost only and comes with a year warranty.
So I dropped it off with Apple, and picked it up today. What I didn’t realise is the whole bottom case is new too. New keyboard, trackpad, bottom as well as the battery. It all comes as one kit.
So pretty happy, I now have a very ‘new looking’ old MBP.
I left without looking at the new M1 Pro/Max ones. Didn’t want to be tempted 