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I have a USB-C powerbank. That is, a battery pack with a USB-C cable that can be used for charging the powerbank, or for charging other USB-C devices from the powerbank.

If I plug the powerbank into my phone's USB-C port it'll charge the phone, but I can tell my phone to charge the powerbank instead.

If I plug the powerbank into any of my MacBook Pro's USB-C ports it'll charge the laptop. Is there any way I can tell my MacBook Pro to charge the powerbank instead?

I know I can charge other USB-C devices, like my phone or iPad, from my MacBook Pro's USB-C port.

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    "Is there any way I can tell my MacBook Pro to charge the powerbank instead?" Plug your Mac into a wall-charger?
    – Seamus
    Dec 29, 2023 at 6:03
  • Your powerbank is dangerous. I had a similar one. One particular day, when I wanted to charge the phone, it kept draining it instead. I didnt realise it until the phone battery was exhausted. Stupid concept. I got rid of it. Now I have one where the socket is for charging and cable is for supplying power. Feb 3 at 4:25

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One possible way to switch the direction of power flow is to unplug the cable temporarily and plug it back in. There's a bit of a "memory" with Apple devices and how it deals with peripherals that allow for power to flow in either direction, if the power isn't flowing the direction you like then a "reboot" by unplugging and plugging back in will sometimes reverse the power flow. Some devices will have a preference for supplying power if the connected device will accept power, in which case there's another tactic to try.

With a USB-C/male to USB-A/male cable, and a USB-C/male to USB-A/female adapter one can construct a kind of USB-C to USB-C cable. That USB-A connection in the middle though will dictate the direction of power flow as USB-A does not support bi-directional power flow like USB-C.

The USB-A connection will limit power flow to 12 watts, which should not be much of an issue since the USB-C ports on a MacBook Pro will supply either 7.5 or 15 watts maximum depending on the specific model and any other connected loads.

I've heard of people trying to charge USB-C power banks from a laptop before and see the power bank charge and then discharge. It seems that if left unattended the decision on where the power should go gets "reset" by either device because once the state of charge on the power bank reaches full then one device or the other decides to transfer power in the reverse direction. A USB-C cable with that USB-A connection in the middle will avoid this because reversing flow of power through that USB-A connection is not allowed.

There may be USB-C to USB-C cables that have some hardware that restricts power flow to one direction but that would be a cable that doesn't comply with the USB specs. I could see such a cable as convenient but by lacking that USB trident logo to indicate it is up to spec I might not trust it.

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