Help understanding USB-C charging


macrumors member
Original poster
Jul 31, 2008
I finally made the decision to bite the bullet and go to a new touchbar mac. I wasn't wanting a touchbar, but wanted a new 15" screen.

I have been doing some trial and error tests with charging this thing. I hate the dongle hell that I am going through with USB-C, but it seems to be worth the trade off by getting more flexible charging. I am off the grid quite a bit.

I have found some USB-C external batteries, but none that are 87 watts. I have an Anker Powercore II 20,000 and have found that it will charge my 15" MBP, but only if it is off (sleeping) at the time. I use a USB A to USB-C cable to achieve this. So I am asking for some help understanding how this all works.

1. Does it matter that I charge USB A to USB-C other than speed of charge? In other words, does USB-C to USB-C offer anything more than faster charging speeds?

2. Does it "hurt" my battery to charge very slowly off of a battery pack? Even if it takes all night I can get another charge the following day.

3. Do you lose anything in the USB A to USB-C conversion in terms of power? I'm thinking do I really need a USB-C port on the battery pack if the only downside is slower charging? If it doesn't damage the battery then I am fine with this.

4. I also have used a USB A iPad car charger to charge my laptop. Does this "hurt" the battery.

Thanks for the help. I'm perfectly happy just using a trial and error approach to figuring out what will work and what will not. I just don't want to ruin my new laptop only to have Apple tell me that anything other than an Apple branded charger shouldn't be used unless that is really true.


macrumors 68030
Apr 25, 2012
I strongly caution against using the A-C charging. A USB-A port can only output 2.4A at 5V, a little over 10W, a USB-C (on current battery packs that have it) will output at least 15W if not more. So, yes, you DO lose something when using the USB-A ports.

There are SEVERAL posts on this forum regarding this topic...


macrumors 6502a
Sep 8, 2011
Last edited:


macrumors 603
Nov 3, 2011
SF Bay Area
USB type C charging is not just a simple mechanical connection. There are bidirectional command that determine the capability of the charger, the power requirements of the device and ensure that they are compatible. So get the right charger and cable. Look up USB-C Power Delivery for more information on the spec.

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