
While the iPhone Air MagSafe Battery is not compatible with any other iPhone models, the USB-C port on the battery pack can charge some smaller accessories.

As noted by 9to5Mac's Zac Hall, the iPhone Air MagSafe Battery product page has this line:
Apple says the USB-C port on iPhones can charge an AirPods case, Apple Watch, or another small device that supports USB Power Delivery at up to 4.5W, and the USB-C port on the iPhone Air MagSafe Battery likely behaves the same way.Charge smaller accessories via USB-C
So long as the iPhone Air MagSafe Battery has a sufficient charge, connecting a USB-C cable from the battery pack to the small accessory will initiate charging of the accessory — it could even be something like a small USB-powered fan.
Apple's original MagSafe Battery Pack with a Lightning port could not charge small accessories like an AirPods case or an Apple Watch in this manner.
You can order the iPhone Air MagSafe Battery now, with U.S. pricing set at $99.
Article Link: iPhone Air MagSafe Battery Can Charge AirPods, Apple Watch, and More