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I have 2015 rMBP and its hooked to a thunderbolt display and uses it's power cord for charging. I noticed that the charging wattage is really low(~2W) compared to what I see when using the MagSafe 2 power adapter(~54W). The wattage actually fluctuates when using the thunderbolt cable. So just wanted to know if this is normal? Or is there anything I can do for this? Would I be damaging the battery this way. I really don't want to use the MagSafe adapter because of how the cables are setup now. Thanks in advance for your help!

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  • I'm confused...you say you are using the TB display's power cord, which is actually a MagSafe (power from the TB display) but you don't want to use the MagSafe. So, which display specifically are you using? How are you getting power? Also, how are you measuring the power draw? Is it an app or do you have test equipment attached?
    – Allan
    Commented Apr 27, 2017 at 15:16
  • @Allan Sorry there is a picture attached but its still being peer reviewed. Here is link to the screenshot(I uploaded somewhere else): jmp.sh/T6ZeVf1 I meant I dont want to use the MagSafe power adapter. Commented Apr 27, 2017 at 15:27

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What you are seeing is the "current draw" for charging the battery. This will fluctuate and is perfectly normal.

example image

You will see this fluctuate more so when the battery is full or nearly fully charged when it doesn't need much current to bring it back up to 100%. When it reaches full charge, there's no need for full current draw.

The 2015 rMBP has either a 60W or 85W power adapter (13" or 15" respectively). 54W draw is well within the limit of either adapter which means (to use a Star Trek: TNG phrase) it's operating within normal parameters. The 54W is just the draw at this particular time; charging the battery and powering the MBP. Crank up some processes (like video editing) and your draw will go up. Turn it off/put to sleep and ~100% of the power will go to charging the battery until it's full.

There's nothing to change nor is anything here harmful to your battery.

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  • It doesnt fluctuate much when the Magsafe adapter is plugged in. Plus the wattage is ~54W which I assume is what its suppose to be. Commented Apr 27, 2017 at 15:38
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    Appreciate the input Allan, but the draw is low even when the battery charge is around 20%. Also I had opened up a few VMs and then the fan kicked in but still the power draw go up. It was still fluctuating below 10W. Not the same experience with the Magsafe adapter(power block) though. Commented Apr 27, 2017 at 16:39
  • You have to keep in mind that the priority is computing first, charging second.
    – Allan
    Commented Apr 27, 2017 at 17:34

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