Huawei Mate 20 Pro's reverse wireless charging was tested and found to be extremely slow
Huawei included the ability to 'Reverse Wireless Charge' with the Mate 20 Pro. This feature allows the user to charge other devices with wireless charging capabilities by placing them on the Mate 20 Pro's back panel. It seems an innovative use of the new phone's 4,200 milliamps-per-hour (mAh) battery. However, when an Android Authority contributor decided to test Reverse Charge for himself, he was somewhat underwhelmed by the invention.
This correspondent (Robert Triggs) reported that his Mate 20 Pro was very slow to charge a Pixel 3 (which can charge via wireless or wired connections). Triggs then compared the phone's charging rate with that of the Pixel Stand or a standard USB type C cable. This was done using AccuBattery, a diagnostic app for Android.
The writer also noted that this app showed the Pixel 3 charging by 1985mAh and 10 watts (W) using the Pixel Stand, and by 2815mAh and 15W through the USB cable. By contrast, this phone only charged at a rate of 594mAh when placed on the Mate 20 Pro. Replacing the Pixel with a phone that defaulted to use 5W when placed on the Stand (the LG V40) resulted in a charge rate of 1078mAh, compared to 509mAh when using the Mate 20 Pro. Therefore, Triggs calculated that the Huawei phablet 'reverse charged' at about 2.5W.
This test, while possibly not very extensive or accurate, demonstrates that the Mate 20 Pro can charge another device, but not very well compared to a real, official wireless charger. It is possible that its users should reserve this feature for devices with smaller batteries, such as the Freebuds 2 that Huawei designed for use with the 3.5mm jack-less Mate 20 Pro.