how to stop reducing battery health

Batteries degrade over time with usage, that's just how they work. You can expect about a 1% drop per month with average use on an iPhone.

Apple recommends replacing it when it reaches 80%

Here are some tips on maximizing battery life.

https://www.apple.com/batteries/maximizing-performance/

Hello ~ Take a look here:

Batteries - Maximizing Performance - Apple

You are fine on battery…if it drops to 80% or below

iPhone Battery & Power Repair - Apple Support

~Katana-San~

Hello ~ You are doing fine …stop worrying and reread this by clicking on the blue link:

Batteries - Maximizing Performance - Apple

~Katana-San~

Hello again ~ You actually are doing fine with your battery…don’t worry and enjoy your iPhone. If it drops below 80% simply get it replaced… you are okay :)

~Katana-San~