Battery-powered 2018 MacBook Air will only negotiate Thunderbolt for first connected device
I've found an interesting thing: when one device (of any kind) is plugged into a USB-C/ThunderBolt 3 port on my 2018 MacBook Air while on battery power, the second port will only let things connect as USB.
A few scenarios to illustrate this:
- Thunderbolt 3 Hard Drive plugged in = another Thunderbolt 3 hard drive won't mount until first one is disconnected.
- USB 3.x dock/hub plugged into Port 1 = Thunderbolt 3 hard drive won't mount when plugged into Port 2 until Dock is disconnected.
- USB 3.x Dock/Hub plugged into Port 1 = Hard drive capable of both TB3/USB3 will negotiate a USB3 connection.
- BUT... if Thunderbolt 3 Drive is plugged in first, then that same USB 3.x dock/hub will plugin and mount correctly.
If the MacBook Air is powered – say, via a Power-Delivery-Capable TB3 or USB Dock – then both ports will negotiate a Thunderbolt connection regardless of what else is plugged in.
I've confirmed this on two different 2018 MacBook Airs, so I know it's not some anomaly with one.
It seems, perhaps for power consumption purposes, Apple has configured the 2018 MacBook Air to only negotiate a Thunderbolt 3 connection for the first device plugged in when on battery power. Maybe?
My question: do Apple's other Thunderbolt 3 laptops behave the same way? Anyone with, say, a 16" MacBook Pro (or even a 13" MacBook Pro) able to test and report?