How to diagnose new iPhone 13 Pro battery issues?

The iPhone 13 Pro was discontinued in September 2022, so the phone that you purchased was at least 2+ years old and as much as 3+ depending on when the phone was manufactured.

Did the model number indicate that this might be a refurbished phone?

There is no way that a 3 year old phone would display a battery Maximum Battery capacity of 100% unless the battery was very recently replaced.

The iPhone 13 battery was designed to handle up to 500 Charge Cycles before the battery reached 80% Maximum Capacity. 1190 Charge Cycles with a Maximum Capacity reading of 91% cannot be real.

I’m wondering if something like that could have been done before I bought the device.

All kinds of things can be done with refurbished or used phones, especially if the refurbishment process was done by a non-authorized Apple shop.

Might be a good idea to take the phone in to the Genius Bar or an authorized Apple service shop, so they can run some checks and tests using their own equipment. Might be some interesting results.

The Model Number of the phone can possibly provide clues regarding the status of the phone.

What is the Model Number? Settings > General > About > Model Number (Please do NOT post the serial number.)

Since we know that the phone is at least 2+ years old and as much as 3+, I think you can understand why it is extremely unlikely that you bought a "new" phone. If the phone really was "new", it must have been sitting in a warehouse somewhere for 2-3+ years. The battery would be in really bad shape if this was the case and it would be remarkable if the phone would even power up at all.

Tap Settings > General > About and look at other categories like.....

Warranty Coverage

Parts & Service History

What information is displayed regarding these categories?

The Model Number of your phone indicates that it is a used phone, not refurbished. The phone is anywhere from 2+ to 3+ years old.

It is likely that the battery was replaced in the iPhone, but whether or not a genuine Apple battery was installed, we cannot say.

What about Warranty Coverage details? So far, it sounds like coverage has expired.

Is there anything there about Parts and Service History? If the battery was replaced with a Genuine Apple battery, this information would appear here.

You can also learn more about the phone if you use this link:

Check your device's coverageAppleCheck Your Service and Support Coverage - Apple Support

Yes, battery statistics can be manipulated in non-Apple batteries. YouTube probably has videos showing how it’s done.