Battery drain

Check Settings > Battery > Battery Health

If that percentage is below 80%, you should probably replace the battery.

see if this support article helps

Batteries - Maximizing Performance - Apple

One of the biggest draws I see on my battery life is if I'm working in an area with poor cellular reception that day.

When this happens, I will try to remember to turn my phone to airplane mode.

Do you work in an area with poor cellular reception?

Reduce the brightness, turn off WiFi, use Optimized Battery Charging.

I found some useful information in this article about iPhone battery health and if you want to dig deeper - here are some more technical explanations.

What is your battery health now?