I was told that the battery has to qualify for battery replacement on some devices. That's because they don't replace batteries on an iPad Pro - they always replace the entire device so unless you quality for the battery program, your only option is device replacement. Which they will do if I want but at a much greater cost. That's almost 1/2 the cost of what I originally paid for it.
I was told this directly by an Apple store employee this week. He said he literally can't select the battery replacement option unless he can prove that it is the battery and without the health report saying so, he doesn't know any way he could.
If that doesn't work out, easiest thing is probably to sell on Craigslist with some disclosure and buying a new one.
For the Airpods Max they currently list a price of 87€, but as far as I understand there's only one battery to swap. But 87€ every few years is still a high maintenance price, hoping they don't increase that price.
Also, Apple only offers service for a few years. I have a few bloated Macs that would need a new battery but Apple just doesn't service them anymore.
For many devices you can get replacement batteries from 3rd party sellers, but quality is hit or miss -- there's no guarantee the replacement battery is going to last (but in my experience Apple's replacement batteries are also unreliable sometimes).
Most of my Hifi gear is more than 15 years old. I doubt any of Apple's new audio products will last that long.