As many have mentioned the policy varies.
From personal experience, I bought a used iPad 6th Gen back in 2020. The seller didn't disclose it but the battery health was at around 80 something percent, I think 85%. The battery was draining pretty quick, and it was far under the 10 hours that Apple rated for the model. Since it was out of warranty, I reached out to Apple willing to pay the battery service fee of $99. Because it wasn't low enough per their own standards, even through I was willing to pay they refused to do anything with it. I tried escalating it, and spoke to a bunch of folks but it didn't feel like I was getting anywhere. So I ended trading it into Best Buy (at a loss for what I paid for) and getting a new device.
That's one of my biggest criticisms with Apple, if the batteries aren't user serviceable then the user should have the right to pay for a battery replacement outside of a warranty related issue. Apple shouldn't just arbitrarily be able to say, your battery life has decreased but hasn't decreased enough by our standards for you to pay us to do something about it. There are users that need the full 9-10 hours of battery life and have an unusable device if it's only lasting 6-7 hours, for example they could be using the iPad at a job site where they might not have access to an outlet. If an iPad is supposed to be a portable computing device then having the full rated battery life is key, otherwise it's just another disposable toy. *gets off soapbox*