Battery capacity bad?

Wherever I bought the cell phone, it was always in ultra power saving mode for 265 hours. Why is it so little now? What can that be?

Cell phone is a Huawei P30 pro 128gb

There are probably some apps running in the background.

Did you treat the battery well? So do not use it while charging, ideally do not charge your mobile phone overnight, etc.

Yes, I only have WhatsApp and Ebay classifieds on it. The cell phone is 3/4 year old

Then apps are open in the background or something else is happening in the background. But since i can't help huawei is not my field sry

Can have many reasons.

brightness
Set functions
Wi-Fi, Bluetooth, mobile data etc.
Apps (active as in the background)
wear

I deactivated everything except the Huawei apps and WhatsApp