that isn't correct but the BMS on the truck counts all the amps in amps out of the batteries so you are supposed to hook positive to a battery and negative to the frame or engine IF you have the amp meter on the negative passenger cable or else you will have issues. same with accessories...
ford has videos online where they leave em sit in a giant arena size freezer at -40 for days then cold start em to do tuning and make sure they will start. i dont even bother plugging it in now i just set the timer through the app so it starts and warms up while I'm in the shower.
its accurate enough that i wouldn't waste the money on the hitch but its not precise and it can be affected by other things. it doesn't take very much tools in the bed to throw off how much tongue weight it thinks your trailer is adding and i dont know how accurate they are going to read once...
my 17 worked great, the 21 is a bag of dicks for call quality. i blame it on ford cutting costs. yesterday i got one of the auto updates now it won't even connect calls, plays music from the phone for 1 minute then cuts out, no ford connect