Charging Tips

The single most important thing you should do (or rather, not do): Don’t let the battery go to zero and shut off the phone. Doing that regularly will shorten the phone’s battery life, so charge when it reaches 20% just to be safe. Nothing much else will make a measurable difference. Charging overnight with Optimized Charging turned on will extend lifespan a little, but the primary cause of declining battery capacity is simply using the phone. And it’s not a big deal; if the worst happens Apple will replace the battery while you wait. Free if it reaches 80% within the warranty or AppleCare+ extended warranty, $69 out of warranty.

See: When to charge your iPhone or iPad - Apple Community

It is not possible to have 100% battery capacity forever.

As stated: there is no need micromanage the charging process. There is no need to charge to a specific percentage. The key thing to remember is to not repeatedly deplete the battery to low levels. Other than that, if you charge it to 100% (yes, you can and should do that) and it lasts the full day, you are fine. Otherwise, charge as is required.

No. But why would you need to be constantly plugging/unplugging?

Read the user tip posted above.