It looks like Google plans on adding reverse wireless charging feature to its upcoming Pixel 5 smartphone. References to the feature have been found in the first Android 11 Developer Preview. There is a new activity in the Settings menu called "Battery Share." The attached strings with the feature make it clear that Google is working on reverse charging feature for its future Pixel smartphones.
The strings for Battery Share state that "your phone"s battery will run out faster when using battery share. Battery Share works with compatible ear buds, watches, phones, and more." While reverse wireless charging is not mentioned explicitly here, the text makes it clear that this is what Battery Share is all about.
Another reference found in the Android 11 Developer Preview makes it clear that the Battery Share feature will be found in "redfin." Some details about this device have leaked previously. This device is possibly a mid-range Pixel 5 variant that Google is working on with a Snapdragon 765 chip.
The Google Pixel 3 and Pixel 4 series support Qi wireless charging, but none of them feature reverse wireless charging. Google can"t enable Battery Share on these phones with the Android 11 update as they lack the necessary hardware. Reverse wireless charging has become commonplace in flagship smartphones from Samsung, with the Galaxy S10, Note10, and S20 series packing it. Huawei"s flagship P30 and Mate 20 series of smartphones also feature reverse wireless charging. The feature can come in handy when you are on the move and need to charge your earbuds or other small accessories that can charge wirelessly.
Source: XDA Developers