Apple says
Do we have to?
And also its status light seems to be off after a few seconds. Does that mean it’s no way to know whether it is fully charged without attaching to an iPhone?
Before you use your MagSafe Battery Pack for the first time, fully charge it using a Lightning to USB cable with a 20W or higher power adapter.
How to use your MagSafe Battery Pack - Apple Support
Your MagSafe Battery Pack is designed to quickly and safely wirelessly charge iPhone models with MagSafe, giving you more time to use your device.
support.apple.com
Do we have to?
And also its status light seems to be off after a few seconds. Does that mean it’s no way to know whether it is fully charged without attaching to an iPhone?