Saw some spotty information on this online - but not sure if it's built in, what years, and if it's an accessory for this generation.
Trust me, you dont want it. Dont make it a need on your wish list. I actually disconnected mine so I can use the tray for coins and other metal objects. The Gen 4 charges at less than 1 Amp (says 1A on the back of the module, So that includes what the module it's self draws. if my Note 5 is idle with no programs running, it will keep the battery from discharging, but thats about it. Also the first bump you hit that moves the phone interrupts the charge and errors out the charger. Only fix (i found) is to remove phone, turn unit off, wait 3 seconds, turn on unit, place phone down and wait for the next bump to repeat the process.
You can buy a Qi charger for the Gen 3, I have seen them on Croooober. But you don’t want it. My iPhone 8 is Qi enabled, and idle it will maintain the charge, but if there are apps running in the background, the battery will run down.
I have a Scosche Qi mount that I bought when my samsung phone stopped charging via the USB cable. It works well and will even bring the charge up from a low level while running apps and keeping the screen on at full brightness. After cleaning the usb port several times, the port will now charge on a USB cable again but I continue to use the Scosche mount when in my car. I can see how a tray would not work well unless it had multiple coils in it.
