Apple phone battery and warranty

[ImAvingOops]

I have just had dd's battery replaced in a phone I bought from an Apple store in Aug 2020 (which offers a 2 year warranty)and have had to pay £49. Apple say that because the battery hasn't actually died, I have to pay this cost. But, we had the notification from Apple that the phone needed servicing as it had dropped below 80% and the power was only lasting a few hours with normal usage. So not really fit for purpose.
Aibu to think that Apple should cover the cost of replacing the battery on a phone which is still less than 2 years old?

Do you have apple care as I remember being told its covered if it drops to 80% with that. I think the money you have paid would be the insurance excess cost?

I just have the standard warranty. Have already had to have the camera replaced earlier in the year, although that was covered. Just seems a lot to spend on a phone that's less than 2 years old!