Apple's iPhone 15 and iPhone 15 Pro models use a USB-C port instead of a Lightning port for charging and data transfer purposes, and the new port allows the iPhones to charge a wide range of USB-C devices, including another iPhone.

As demonstrated by Marques Brownlee, plugging a Lightning based ‌iPhone‌ into a USB-C iPhone 15 with a USB-C to Lightning cable lets the ‌iPhone 15‌ provide power to the older ‌iPhone‌.

When you plug a Lightning ‌iPhone‌ into an ‌iPhone 15‌, the ‌iPhone 15‌ will always provide power to the Lightning ‌iPhone‌, even if the ‌iPhone 15‌'s battery is lower.

If you plug an ‌iPhone 15‌ into another ‌iPhone 15‌, the two devices communicate with one another, determine which ‌iPhone‌ has the lower battery, and transfer power that way. So if you have a low battery and a friend with an ‌iPhone 15‌ has a full battery, you can plug your ‌iPhone‌ into your friend's ‌iPhone‌ and get yours to charge.

With a USB-C Android phone, if the Android device has USB Power Delivery support and you connect to an ‌iPhone‌ with a lower battery level, the Android device will be able to provide battery power. If the Android phone does not have USB PD, the result is inconsistent and there's no way to predict which phone will be the charger and which will get the charge.

The ‌iPhone 15‌'s USB-C port can be used to charge an Apple Watch or the AirPods Pro 2 with USB-C Charging Case using a USB-C to USB-C cord, and it should also be able to work with most other USB-C devices in some capacity.

Unfortunately, when charging another device with an ‌iPhone 15‌, the charge is limited to 4.5W. That's appropriate for small devices like the Apple Watch, but it's not going to provide much power for an ‌iPhone‌, so expect slow charging speeds when using ‌iPhone‌ to ‌iPhone‌ charging functionality.

Source: Macrumors