iPhone 14 Pro battery percentage decreased by 3% within a week

The iPhone 14 Pro was discontinued in September 2023, so your iPhone is at least 18 months old and as much as 30 months old depending on when the phone was placed into service.

How old is your phone?

What is the current Maximum Capacity of the battery?

On average....over longer periods, the Maximum Capacity is expected to decline at about 1% a month. But...that is an average. It is not unusual for the battery to sometimes not decline for 2-3 months, and then drop 2-3% the next month.

If you're talking about the Maximum Capacity percentage, that value is related to when the battery (not the iPhone) was new, it's caluculated in charging cycles (1 cycle = charging from 0 to 100%, and it depends on many factors).

See this article:--> iPhone battery and performance

and this user tip:--> When to charge your iPhone or iPad - Apple Community

Regards

Giulio

Your iPhone's battery health decline is not linear, meaning it will not decline at a steady rate but rather an unpredictable rate which can decline a few more or less percent at once. That also means the percentage points can stay steady for a while now.

But the question to determine average battery health decline is how long you have owned this iPhone.