iPad Battery has already swollen up but the Diagnostic test detects no problem

I have an iPad pro 11 inch (2018). I have been using it since Feb 2019, and always feel like the battery is draining, even when screen off.

Since mid Feb 2023, the device just got worse. The screen is popped out from the frame. I believed that it was caused by the swollen battery. So i contacted Apple Customer support trying to get my problem solved.

After 4 visits to 2 different authorized repair stores, 2 phone conversations, 1 chat with the CS staff, it seems that Apple can not offer me an affordable solution. They ran 2 battery diagnostic test, and the test detected no problems with my iPad battery. So if I still want to demand for a battery replacement service, they would charged me at 14m VND (~$594).

*Which they explained to me that if the test detected a problem with the battery, they might give me another device at the price of 2.8m VND (~$120). 

About the iPad batter replacement: iPad Repair & Service - Apple Support

Also, when I went to one of their authorized repair stores in Vietnam (which is listed on Apple website), they don’t even care to run a diagnostic test but offered to replace my battery with another one from a 3rd party at the price of $64. I reported to Apple about this repair store. However, I changed my mind now, I will use their battery replacement service with a hope that they would not destroy the screen TT^TT

After all, I found that all the CS staff from Apple were very nice and they tried their best to help me. However, it costs me so much time and effort contacting back and forth, and eventually, it all depends on the diagnostic test result, not the help of all the staff. 

So my advice is: if you have a problem with your iPad battery, run a diagnostic test on your own. That test result will decide your device’s fate.