This is a function of Google pixel 5 which may interest you if you have devices compatible with the wireless charging standard Qi. Google has indeed implemented a system that allows one of his last two smartphones to turn into an automatic wireless charging station as soon as you connect it by USB Type-C to a power outlet or by USB.
This will allow you to reload Pixel Buds 2020 wireless headphones – or another Qi-compatible smartphone by placing it directly on the back of the Pixel 5 which, for its part, fills up at the outlet.
Google gives all possible explanations on how charging works on a dedicated web page.
When your Pixel phone is plugged in and charging, battery sharing turns on automatically for a short time [NDLR : 30 secondes].
If your phone doesn’t detect that another device is using its battery during this time, battery sharing turns off automatically.
It is automatically deactivated as soon as the battery of the device to be recharged is full.
Once the Pixel 5 is unplugged from the mains, the charging function is cut off. However, you can activate it manually while you are on the move (via the menu of Settings). The Pixel then turns into a backup external battery but, beware, by using it too often like this, its charge gauge risks melting like snow in the sun.