Battery

It doesn’t matter; You can charge it from any level to any other level. The only thing to avoid is draining it to zero, where it will shut off. So it’s safest to charge it when it drops below 20%.

The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates. Here's more information→About Optimized Battery Charging on your iPhone - Apple Support

Chris beat me to it.

See this, When to charge your iPhone or iPad - Apple Community

I appreciated your User Tip. I had to share.

Thanks. Did you see my post from the NY Times in the WC today?

No, but I will look now.