I concur, Apple's denial is seemingly silly, though @spiderman0616 may be possible line as to why. Anyway.. If it does require the battery health to be less than 80% before they will agree to perform the service, it should be stated -- and I'm not seeing it. I do see a mention regarding AppleCare+ service and that requirement but nothing concrete, even a strong implication, in the case of out of warranty, paid service.It comes down to Apple not willing to offer a paid service they list on their website. I went to the Apple Store yesterday and it was denied as well due to Apple's arbitrary test. It's a potential safety and fire hazard if the only options consumers have are to get it done at a 3rd party where the condition of the battery and quality of work are unknowns. It's not like I'm asking Apple to replace it for free, Im more than willing to pay a reasonable price for this service.
iPad Repair and Service - Apple Support
Need to repair your iPad? See your service options, their costs by coverage type, and how long they take.
support.apple.com
Apple said:If your battery has an issue that's covered by the Apple Limited Warranty, AppleCare+, or consumer law, we'll service your iPad or Apple Pencil at no additional cost. Our warranty doesn’t cover batteries that wear down from normal use. If your battery wears down, we offer out-of-warranty battery service for a fee.
If you have AppleCare+, it covers your iPad or Apple Pencil for no additional charge if your product's battery holds less than 80 percent of its original capacity. We might need to test your product to find the cause of your battery issue.
Best Buy is an Authorized Apple Service Provider, although, they don't post specifics, you'd need to contact them with your inquiry.
Apple iPad Repairs: iPad Screen Replacement - Best Buy
Trust Best Buy’s Apple-trained Agents for authorized iPad screen replacement, iPad battery replacement & other Apple iPad repairs at a location near you.
www.bestbuy.com
Lastly, I'll again agree with the suggestion by others of analyzing the battery usage reports to locate any possible problematic apps/services.