Hey there Tiredd,
There are a lot of factors that go into your battery life and performance. Some of these factors include the overall age of the battery, as well as the individual way you use and charge your device. And since your battery is considered a consumable part, it is expected that its performance will change over time and with use.
If you have concerns over the current battery life and performance of your iPhone, we recommend reviewing the information outlined in the Apple Support articles About the battery usage on your iPhone, iPad, and iPod touch - Apple Support and iPhone Battery and Performance - Apple Support. They will provide insight into how your battery works, expected behaviors, and even recommendations to help get the most out of every charge.
Should your battery life still be shorter than expected, we encourage you to reach out to Apple Support directly. They will have access to additional tools and resources needed to provide additional information and options related to your battery. You can do that here: Get Support.
Have a fantastic day!