Battery health from 98% to 89% in short time

XS is not a "new' phone, since this model was discontinued by Apple in September 2019. Even if the phone really was "new", it has been sitting in a warehouse for more than 4 years.

You likely have either a "refurbished" phone or a "used" phone.

I would be really suspicious about a reading of 98% Battery Health on a 4+ year old iPhone. If the phone was "refurbished" the service company can play tricks with the battery to make things look a lot better than they really are.

If the Battery Health really is 89% now, this means the battery was likely replaced in the phone 12-18 months ago, so you would be looking at a new battery replacement in another 9-12 months or so.

I did not say that 89% was bad. This indicates that a new battery was installed 12-18 months ago.

I did say that i was suspicious of a battery that read 98% 3 days ago. If the battery drops another 8-10% in the next month or two, the battery is definitely defective.

Hopefully, the phone came with some warranty coverage....just in case.

Did you read the part in my reply about the "refurbishing" companies playing tricks with the battery to make things look better than they really are for a time? After a week or two, the battery no longer looks very good at all.

If the battery was really at 98% a few days ago.....(I do not think the 98% really was accurate).....and it is now at 89%.....then the battery is defective, and you will need a new battery in another month or two.

You might want to think about possibly returning the phone for a refund as well.

The iPhone XS was last sold in 2019. If it is original, the battery is likely going to run out just due to age.