Can iPhone charging case be charged alone or does it need to be on the iPhone

Hello,

This is only relevant for the Smart Battery Case. If you use a 3rd party case check with the manufacturer.

Charge your iPhone with your Smart Battery Case - Apple Support

"Charge your Smart Battery Case

Before you start using your Smart Battery Case, update your iPhone to the latest version of iOS. Also make sure that you charge your Smart Battery Case before you use it.

1. Plug the Lightning to USB cable that came with your iPhone into the Lightning connector on the case.
2. Plug the other end of the cable into an Apple USB power adapter, then plug the adapter into a power outlet. For the fastest charging, use an Apple USB-C power adapter that provides 18 or more watts of power.
3. You'll see an amber status light while the case is charging. When the case is fully charged, you'll see a green status light."

I hope this helps.