The iPhone 12 could be Apple's first iPhone with reverse wireless charging, based on a new patent.
A patent filed with the USPTO (via TechRadar) and published on April 9 2020, describes "Inductive Charging Between Electronic Devices." This is a feature that we've seen on Android devices, which allows phones like the Samsung Galaxy S20 or the Huawei P40 Pro to donate power from their batteries to another phone or an accessory like a pair of earbuds or a smartwatch.
Apple has offered wireless charging on iPhones since the iPhone 8 and the iPhone X launched in 2017. However, none of its products provide wireless power, though Apple does appear to be working on bringing its cancelled AirPower charging mat back from the dead.
As you can see from the illustrations, Apple could bring reverse wireless charging to its iPhones, iPads and MacBooks, with the ability to stack multiple devices on top of each other to charge them simultaneously. The patent also suggests that this technology could be used to charge your laptop with your phone, although this probably wouldn't prove an efficient use of your phone's battery considering how much power laptops need to run.
A previous report from 2019 claimed that the iPhone 11 series was meant to get reverse wireless charging, but the feature was disabled in the phone's software because Apple wasn't satisfied with the performance. It's possible that Apple could switch this feature on as part of an iOS update, or debut it on an upcoming device such as the iPhone 12.
If Apple is indeed planning reverse wireless charging, we may hear about it at June's online WWDC 2020 event, or at Apple's usual September iPhone launch event. WWDC is still on track for June as a livestream-only show; no word yet on whether the coronavirus pandemic will affect the expected September event.