When the Mi 9 is fully drained and kept off, we connect the phone to the Xiaomi 20W Qi Wireless Charger which is connected to the Xiaomi 27W QC3 Charger shipped with the Qi charger. Note the Xiaomi 20W Qi Wireless Charger uses Qualcomm Quick Charge technology to communicate with the Xiaomi 27W QC3 Charger.
During the “Fast Charge” mode, the Qi charger consumes around 23W while during the “Cool Down” mode, the Qi charger consumes either at around 13W or 16W levels with the phone's external temperature (which is recorded using a FLIR camera) increasing by 12° C. Finally, in the “Saturation” mode the Qi charger gradually pulls less power until the phone’s battery reaches 100%.
We now repeat the same testing and analysis, but this time with the Mi 9 drained to 1% and with the display and WI-FI kept active. Here, we see that during the “Fast Charge” mode, the Qi charger consumes around 13W for a brief period of time before going into a “Cool Down” mode where power stays at around 10W to 12W range, with max increase of temperature to 22° C. In "Saturation" mode, the Qi charger steadily reduces the power drawn as the battery reaches 100% charge, with the display and WI-FI kept active.
Comparing how the Mi 9 charges when the phone is off versus when the display and WI-FI are kept active, we can see that the phone charges faster as it pulls more power initially when off. When off, the Mi 9 charges in about 1.9 hours versus 2.3 hours when the phone's display and WI-FI are kept active.
Comparing the Mi 9 while the phone's display and WI-FI are kept active, charging using the Xiaomi 27W QC3 Charger versus the Xiaomi 20W Qi Wireless Charger, we can see that the phone charges in about 1.5 hours versus 2.3 hours respectively. We also observe the phone pulls more power when charging using Quick Charge.