Why my battray is fast low helth?

The measure of battery health deterioration/drainage is subjective and can vary depending on individual usage patterns. There is no universal standard to determine whether the battery health deterioration/drainage is normal or abnormal because it heavily relies on how the battery is used and maintained.

Protect & Prolong the Life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance

Because batteries are consumable parts and with every battery charge, its health will decline and you CANNOT stop it from declining. You can reasonably expect a decline in Battery Health of about 1% per month of ownership. But its decline is linear, and it can remain steady for a while, then drop a couple points. If you've owned your iPhone longer than 3 months, your battery is doing GREAT and it is not something you should be concerned with. As I've already said, your batteries health will continue to decline. When it eventually declines to 80% or less, which it most assuredly WILL do, it will then be time to pay Apple to replace the battery in your iPhone. Until then, stop worrying about something you can't change.

Today I’m update my phone iPhone13 ios 17.1 Update after my mobile battery health 100%

update before 98% today and current battery health 97% way?