I have 90% battery health on brand new MacBook air m3 15”

Return it before the return window closes.

What is shown by the Apple tools?

System Settings > Battery > tap the ℹ️ next to Battery Health > percentage

Image cropped, rotated, and re-posted for readability (more):

juraj228 wrote:

90% battery health

So to confirm, the Apple System Settings shows 90% battery health?

This is the Apple display I’m referencing, and not the third-party tool you’ve shown.

If the Apple battery health display using the Apple System Settings display shows 90%, return the Mac.

juraj228 wrote:

Diagnostics show code PPP020

What is the battery health shown by the Apple battery health display? Not that shown by the third-party app.

System Settings > Battery > tap the ℹ️ next to Battery Health > percentage

FYI, you should make sure the pictures are properly oriented so we can actually read them. It is so simple to do this on an iPhone/iPad by using the instructions in the following Apple article (I'm sure an Android device has similar options):

Crop, rotate, flip, or straighten photos and videos on iPhone - Apple Support

I don't know what app that is you are using so I don't know if it is actually gathering the correct information from macOS for the Battery. If it is, then that picture is showing the Battery Health at 56% of its original Design Capacity. I've only ever used Coconut Battery which has been around for years.

Use the following Terminal command to retrieve the actual battery values from macOS itself (copy & paste this command since it will not work properly if it is not typed correctly with every space as is):

ioreg  -w0  -r  -n  AppleSmartBattery  |  grep  -E  '"AppleRawMaxCapacity"|"DesignCapacity" = '

Battery Health % = (AppleRawMaxCapacity / DesignCapacity) * 100

I agree with @MrHoffman to return it within your 14 day window. That Battery is definitely bad and your third party app seems to be giving an accurate assessment.

If you miss your 14 day return window, then this battery should be replaced under warranty which should not be a problem if the Apple Diagnostic fails the test or the Battery Condition reported by macOS is shown as "Service Recommended".

Did you buy directly from Apple or from a reseller?

I am already suspicious of the provenance of that Mac. Please use this Apple support page to see its warranty status and report what you find BUT do not post the serial number here.

Check Your Service and Support Coverage - Apple Support

No, that strikes me as abnormal. I have never seen any new or refurbished Macs with anything less than 100% battery health. I'd return it.

If it is refurbished, maybe it came like that. If not contact Apple immediately so they can give you another one.