I've got a MacBook Pro 13" 2017 – two USB-C Thunderbolt 3 ports. It came with a standard USB-C cable to support power supply. If I plug this cable into both USB-C Thunderbolt 3 ports the Mac seems to think it's connected to a power supply. IMHO it's dangerous for battery in laptop, but I have to ask: is it any risk?
What can happen to my MBP if I plug this one cable between both of its USB-C ports?
Best Answer
There isn't any risk in doing this, but it'd be a self-defeating practice. Basically, what happens to your MBP will depend on which of the following scenarios is true:
Also, according to Apple:
Source: https://support.apple.com/en-us/HT207256
Finally, the MacBook Pro (15-inch, Late 2016 and 2017 models) and MacBook (13-inch, Late 2016 and 2017, Four Thunderbolt 3 Port models) can power two devices that use up to 15 watts, and two more devices that use up to 7.5 watts. It doesn't matter which side of your MacBook Pro that they're connected to—power is delivered on a first-come, first-served basis.
In the case of your MBP, it can power one device that uses up to 15 watts and one device that uses up to 7.5 watts. However, this will have no impact when connecting the MBP to itself, beyond what I stated at the beginning of my answer.