Battery health

It would have to be under the 80% battery health threshold, and also under 500 complete charge-discharge cycles. Think of it like a vehicle tire warranty. A warranty claim can't be made until the tread reaches the wear bars. There may also be a time limitation. Anything in between doesn't trigger the warranty.

Also - 80% battery health as reported by iOS isn't the official number that Apple uses. When I got my battery replaced, the battery health sampled by Apple's diagnostic was the official one that was recorded in Apple's database. It was a few percentage points lower than what iOS displayed.

And a rough estimate for most people is that they run about 25 cycles per month, so a linear approximation is a drop of 1% every month being considered expected. Some do better, and some do worse, but the warranty won't replace the battery unless the health goes below 80% within the warranty period (with less than 500 cycles) or if there's some other battery failure such as swelling.

But it's rare for anyone to get a battery replaced under warranty. Normal wear doesn't count as a defect.

That wouldn't be a sign of anything particularly wrong. Some iPhones hold off on reporting their battery health decline, but there's no predictability to it.

My Phone is doesn't use this card.

If your battery falls below 80 percent health in one year, Apple will replace it under warranty. If your health falls below 80 percent after that time, you can pay to have the battery replaced.