How to determine if my Battery is defective

[Merchant]

At battery saver mode from 40% below, and at constant ultra durable mode. No games since I use my zenfone 8 for business purposes.

My battery does not survive the day. My screentime today is as attached but already at 48%. And I set limit to 90% charging since purchased. My phone is 6 days now since I bought it. Using android 13. 

Is it defective? Or is this how zenfone 8 really is with the 4000mha. It also heats up while charging at steady mode, I only use the Asus charger. 

[Iceman11]

When checking Settings--->Battery--->Battery usage, what are the top apps using battery?

I noticed something that really helps with the battery life:
Settings--->Security and lock screen--->Fingerprint--->Unlock device (click on the name itself, not the button)--->Screen off unlock (turn it off).

Now in order to unlock your device with the fingerprint sensor you have to click the power button to wake up the screen. Also for better consistency of the fingerprint reader I suggest to hide the icon which shows you where to put your thumb.

I think by default the phone is not going into a deep sleep mode because it's constantly waiting for the fingerprint input. Also Asus couldn't fix the pocket mode for years and frequently my phone was trying to unlock itself while in my pocket. Which uses battery.

Regarding the charging, I usually charge my phone up to 100% with an old slow charger (5W) overnight and using the Asus stock charger only when I need fast charging.
I use durable mode with screen forced to 60Hz because of the PWM (only at 60hz you can enable the "low brightness DC dimming option"). Usually I'm able to get full day with >50% battery left at the end of the day. No heavy gaming of course.

[D_IMAN]

Hmm, what about the newfangled rule (or maybe a myth) - charge the battery to 90%, 80%, etc. Like they will live longer?

[Iceman11]

I tried charging the phone to 80%. What I noticed was that it breaks the battery calibration. Also you get significantly less battery life (not just 20% less). Just the voltage drops a lot faster.
I prefer charging to 100%. In the end I don't plan to use the phone more than 4 years so it should not have a big impact.