The MagSafe Battery Pack has a 7.62V, 11.13Wh battery inside, delivering 1460 mAh of charge.
Roughly, the MagSafe Battery Pack may provide one full charge for the iPhone 12/13 mini and a partial charge for the rest of the iPhone 12/13 models. Though designed for MagSafe-compatible iPhone models, the battery pack can be used to charge any Qi-based device, which includes older iPhones and the AirPods. It cannot charge the Apple Watch as the Apple Watch does not use Qi charging.
REVERSE CHARGE:
The MagSafe Battery Pack has a reverse wireless charging feature. This means that if you charge your iPhone, the MagSafe Battery Pack will also charge at the same time. So you can charge both the iPhone and the MagSafe Battery Pack through the Lightning port on the MagSafe Battery Pack or through the Lightning port on the iPhone, and you'll get the same ultimate result with both devices charging up.