Battery Issue

If the battery health is more than 80% then you have nothing to worry about it. Your battery is fine. If you think battery drains too fast, in Settings > Battery, you can check what app(s) consume the most of the battery. See https://support.apple.com/en-ie/HT201264

Maximum battery capacity measures the device battery capacity relative to when it was new. A battery will have lower capacity as the battery chemically ages which may result in fewer hours of usage between charges. Depending upon the length of time between when the iPhone was made and when it is activated, your battery capacity may show as slightly less than 100%.

A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge. Learn more about charge cycles.

Source: https://support.apple.com/en-us/HT208387 (iPhone Battery and Performance)

We’re all users. The only way to find out is to ask Apple. Use the Get Support link at the top of this page and they can do a remote diagnostic. If the battery needs replacement it will be covered by your existing warranty; if not it will cost you $49 or $69, depending on your phone model.