Hey X-1000,
Welcome to Apple Support Communities. Runtime for iPhone batteries can depend on usage. Since you have a concern that your iPhone battery may not be lasting as long as it should, we'd recommend starting by checking your settings using the tips from Batteries - Maximizing Performance - Apple. Changing settings mentioned there such as screen brightness or background app refresh may improve iPhone battery life.
Next, check your iPhone battery's maximum capacity from Settings > Battery > Battery Health to make sure that it is over 80%. As mentioned in iPhone Battery and Performance - Apple Support, "A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions." So if 80% or lower, a replacement may be needed.
Kind regards.