How maintain battery health 100?

Batteries are consumables. They will always wear out. There is nothing you can do to stop that and not much you can do to affect the rate.

In addition to the great articles Alancito recommended, I'd also suggest this one:

When to charge your iPhone or iPad - Apple Community

You cannot. Declining battery health is normal. With charging cycles, battery health will decline. Batteries become less and less healthy with use. Totally normal

sanjo ~ It will be impossible to maintain 100% battery health.

Batteries - Maximizing Performance - Apple

...Found by searching Apple's Knowledge Base.

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