Battery Heath

To learn about maximizing (and the difference between) battery life and lifespan, read this support document --> Batteries - Maximizing Performance - Apple

Read this support article about Phone battery and performance to read about the battery health feature and what is considered normal performance --> iPhone Battery and Performance - Apple Support

Low power mode may help lengthen battery life: Use Low Power Mode to save battery life on your iPhone or iPad - Apple Support

Limnos wrote:

Low power mode may help lengthen battery life: Use Low Power Mode to save battery life on your iPhone or iPad - Apple Support

I meant that in that it means you won't have to charge it as frequently, and thereby stretch out your limited charge cycles.

The Battery Health is just an approximation and is not linear, meaning if it drops 2% in one week it does not mean it will drop 8% in 4 weeks. Sometimes you may even see the Battery Health increase. You should get 5 - 7 years of use from the battery and Apple recommends replacement when it drops below 80%. The cost for replacement is about $99. These are the basic guidelines, so don't worry about minor changes and you should not have to worry about replacing the battery for 5 - 7 years (and sometimes even longer).

All you can do is make sure Optimized Charging is turned on in the Battery settings. Since batteries are typically rated by charge cycles, Low Power mode may prolong replacing the battery a bit by not having to charge it so frequently, but using Low Power mode constantly is not worth sacrificing your user experience to gain a little more life on the battery.

Also read this post by ASC contributor Lawrence Finch which has a very user-friendly explanation of battery features --> Bettery health maximum capacity - Apple Community