I have been using my FP4 since launch and already got 512 Cycles. and I got a Battery wear of 25% (I am using the AccuBattery App and have been tracking my battery since I got the FP4.
The FP4 Battery is advertised with 10% Wear after 547 Cycles.
What can I do better to prevent such high Battery wear ? At What Battery-Wear-Level is a replacement still environmental?
None 
That’s a very generic figure, most often it is 20% after 1000 cycles, don’t forget each cycle is smaller so it speeds up.
Do you fully discharge and fully recharge the battery occasionally? battery monitors are very sketchy?
What do you get from the built in battery monitor? Remove the acc app for a a week and reinstall it to see what new info it comes up with.
Here’s link to test I do on a laptop battery, graphs and tables of data. Early on I had 7% wear over 40 cycles, now it around 4.5% over 70 cycles.
I dunno how accurate AccuBattery is. It tells me I’m at 49,4 cycles, and I’ve had it since basically the first week of owning the phone. Then again, I never let the phone load to 0% and I almost never let it load to 100%.