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EugW

macrumors G3
Original poster
Jun 18, 2017
9,486
6,850
I'm curious, how well does an 18 W charger work for the MacBook? I know that it's possible to charge the 12" MacBook with a 12 Watt iPad charger, but it's really slow, and sometimes isn't even enough to keep up with active usage, especially if there is a hub with USB drive plugged in. However, will an 18 W charger be noticeably better?

I have the original 29 W USB-C charger and that's fine, but as a backup I'm wondering if an 18 W charger would suffice. Part of the reason I am asking is because I'll be buying an iPad Pro eventually and it comes with an 18 W USB-C charger.
 

mj_

macrumors 65816
May 18, 2017
1,289
863
Austin, TX
It will work, alright, but as you've stated yourself it will be comparatively slow. I've tried using my 15W Oculus Quest charger with the MacBook and it took forever to charge it from empty to full, and it barely even charged while I was using it (without any accessories). I would assume that those three extra watts are not going to make a huge difference.

Then again as backup charger it would probably suffice, and be better than no charger at all ;)
 
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chrfr

macrumors G4
Jul 11, 2009
11,033
4,594
Why is it slow if a 18W charger charges the 12.9 iPad Pro just fine ? I think their batteries are comparable.
The MacBook shipped with a 29W charger originally, so 18W will obviously provide less power than the charger which originally came with the computer. The MacBook's battery is also a little bit larger than the iPad Pro's.
 
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k1ckdapro

macrumors regular
Sep 28, 2014
106
15
Luxembourg
That‘s a fact! But I still find it strange to see it charging slower on my 18W charger than my iPad Pro 12.9 which has more battery capacity - I‘m just trying to understand this difference considering the higher capacity of the iPad Pro.
 
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chrfr

macrumors G4
Jul 11, 2009
11,033
4,594
That‘s a fact! But I still find it strange to see it charging slower on my 18W charger than my iPad Pro 12.9 which has more battery capacity - I‘m just trying to understand this difference considering the higher capacity of the iPad Pro.
Read again. The MacBook has a higher battery capacity. The iPad will also charge faster with the 29W adapter.
 
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chrfr

macrumors G4
Jul 11, 2009
11,033
4,594
Read again, my 2017 12.9 iPad Pro (10875 mAh) has a higher capacity than my 2016 Macbook 12 (5550 mAh).
You need to compare watt-hours rather than amp-hours because of the different voltage.
The MacBook has more watt-hours, which is why it takes longer to charge.
Edit: here's an even more concise explanation: https://thewirecutter.com/blog/watts-in-a-name-why-were-using-watt-hours-to-compare-batteries/
 
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konqerror

macrumors 68020
Dec 31, 2013
2,298
3,693
The MacBook also has a higher power consumption. Any power being consumed by the computer can't be used to charge the battery.
 
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