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echo1877

macrumors member
Original poster
Nov 10, 2015
82
107
So we’ve all heard that the iPad Pro is slow to charge, but I’ve been doing some research on the actual numbers and have had some interesting findings. I’m the developer of a battery/charging information app on the App Store called Battery Health and so I am often looking at the innards of iOS devices in terms of batteries and power management. This research is based on live stats reported by the internal charger device driver on the iPad Pro.

iOS devices ship with an internal charger chip (that's inside the device, NOT the power adapter that ships with it) that is configured to charge the battery at certain rates, depending on several factors. Battery charging speeds are typically measured by a unit called C, which is basically a fraction of the total capacity of the battery. For example, a 1000mAh battery that charges at 0.5C indicates that we’re charging it with a 500mA current, or half of its capacity. The higher the charging current, the faster the battery gets charged. For most iOS devices, the base charging rate for the constant current stage (the early, fast stage in the charging process) is around 0.55-0.65C.

For example, The iPhone 6 Plus has a 2855mAh battery and it charges at a maximum current of 1730mA, or about 0.60C. The iPhone 6S Plus has a slightly smaller 2725mAh battery, and its maximum charging current is 1790mA, or about 0.65C, so it charges a bit faster than the 6 Plus. Some Android phones will go much faster, up to .80C or even 1C. The catch is that faster charging shortens the overall life of the battery, so quite honestly Apple is playing it very safe with these kind of numbers, which is why their batteries tend to last so long.

Now, the iPad Pro has a gigantic 10,088mAh (38.3W) battery, but its maximum input current at the USB port is only 2400mA (12W, same as all other recent iPads). When you charge an iPad Pro, its charger is configured at 0.55C, same as many other iOS devices. The problem is that with a 10,088mAh battery, that comes to 5560mA, or 28W.

This means that the iPad Pro technically needs a 28W charger to charge at optimal speed — at the INTENDED speed. The 12W charger it ships with is only supplying 40% of the current required to charge it at maximum speed.

What’s more alarming is the fact that if you push the Pro hard (full screen brightness, LTE video streaming, etc.), its current draw sometimes actually reaches 2400mA! This means that you could be plugged in with the 12W Apple brick while using it, and the battery won’t actually get charged.

Note that as best as I can tell, the device is configured for a maximum input current of 2400mA at the Lightening port (again, that’s what the device is reporting), so be wary of any 3rd party chargers that claim to charge it faster than the stock charger. I’ve not seen anything like that, but it seems like a likely scam…

For now, the bottom line is, make sure to charge your iPad Pro while it is in standby with the screen turned off. It will barely charge while being used, even with the 12W charger.

UPDATE: Apple has now released a USB-C to Lightning cable that allows the use of the 29W MacBook charger with the iPad Pro.
 
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masotime

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Jun 24, 2012
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This means that the iPad Pro technically needs a 28W charger to charge at optimal speed — at the INTENDED speed. The 12W charger it ships with is only supplying 40% of the current required to charge it at maximum speed.

Yes this is very annoying. As a "Pro" device I think a USB-C port which supported charging speeds similar to the Retina MacBook's 29W adapter would have been fully justified. As mentioned in another thread, this would also make charging the Apple Pencil a lot easier....
 

JonSarge3108

macrumors regular
Nov 11, 2015
204
58
Interesting post - thank you

In terms of battery health, is there any downside to charging with an iPhone charger (10W?) or an in car charger?

I know it's slower - but for a bit of a boost if that's all that's around ?

Also, for longevity, should I allow the iPad pro to fully run out of battery then fully charge it or am I ok topping 20% only up each night?

Thanks.
 

A.R.E.A.M.

macrumors 6502
Nov 12, 2015
330
178
Los Angeles, California
lithium polymer devices all have circuitry in them to regulate the charging process. this is not specific to apple. heat is the biggest enemy to charging these batteries, so the manufacturer has to balance charge speed with heat in best case scenarios, so yeah battery charge time may be extended to prolong the battery health and heat generated from these devices.

a 10 w charger will work fine, but if you are using more power than the charger can supply, you will not maintain the battery charge sufficient to charge up to maximum capacity.
 

echo1877

macrumors member
Original poster
Nov 10, 2015
82
107
Interesting post - thank you

In terms of battery health, is there any downside to charging with an iPhone charger (10W?) or an in car charger?

I know it's slower - but for a bit of a boost if that's all that's around ?

Also, for longevity, should I allow the iPad pro to fully run out of battery then fully charge it or am I ok topping 20% only up each night?

Thanks.
Well, an iPhone charger is 5W, not 10W. Older iPads shipped with 10W chargers. None of those will impact battery health either way, but the 5W iPhone charger will charge VERY slowly, and ONLY while the screen is off. Watch what happens when you plug in a 5W charger while the iPad Pro is on:
iPad Pro Insufficient Power.png
Basically, the iPad Pro is consuming about 1875mA in total at that particular moment, 1000 of which are coming from the power adapter, and the rest are coming from the battery...

As for longevity, as always the recommendation is that deep discharges (draining the battery all the way down to 20-30% or so) tend to shorten the life of Lithium Ion batteries. The ideal usage is shallow discharges down to 50-60% if you can help it.
 
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garyleecn

macrumors 6502a
Jul 25, 2014
841
142
isnt mah a unit of work, and when talking about charging, shouldn't we talk about power (i.e., rate of work) instead of work? though i get what you are saying..


so, do you think it's possible that there may be a high-power third party charger that charges ipad pro at 0.5c+? i remember reading the lightning port on ipad pro is actually usb 3.0, shouldnt that allow more power (again, not work lol)?
 

mi7chy

Suspended
Oct 24, 2014
9,993
10,837
12W is quite anemic for a tablet charger. For comparison, Galaxy Note 5 comes with 15W charger and the lower end Surface Pro 4 4.5W Core M3 charger is 24W vs 36W for the normal one. Both charge the battery while the device is in use and even under load. Curious why Apple decided to go so low.
 
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Daku93

macrumors regular
Oct 29, 2010
240
267
I wonder if the maximum charging rate the app reports is correct. Maybe it would charge faster, if you used the retina Macbook charger with a USB-C -> USB Adapter and the Lightning cable…
 

echo1877

macrumors member
Original poster
Nov 10, 2015
82
107
I wonder if the maximum charging rate the app reports is correct. Maybe it would charge faster, if you used the retina Macbook charger with a USB-C -> USB Adapter and the Lightning cable…
The app reports the maximum current allowed on the Lightning port, as reported by the device. All other Apple devices have reported this accurately. For example, the 6 Plus and the 6S Plus both report 2000 mAh, which is exactly right. All recent iPads report 2400, and older iPads report 2100 (10W).

I highly doubt that Apple has a way to fix this in the current model. They'll likely have to switch to a different port such as USB-C in the next model in order to improve this.
 

dyt1983

macrumors 65816
May 6, 2014
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USA USA USA
For example, a 1000mAh battery that charges at 0.5C indicates that we’re charging it with a 500mAh current

[...]

Now, the iPad Pro has a gigantic 10,088mAh (38.3W) battery, but its maximum input current at the USB port is only 2400mAh (12W, same as all other recent iPads). When you charge an iPad Pro, its charger is configured at 0.55C, same as many other iOS devices. The problem is that with a 10,088mAh battery, that comes to 5560mAh, or 28W.

[...]

What’s more alarming is the fact that if you push the Pro hard (full screen brightness, LTE video streaming, etc.), its current draw sometimes actually reaches 2400mAh!

[...]

Note that as best as I can tell, the device is configured for a maximum input current of 2400mAh at the Lightening port (again, that’s what the device is reporting)

Basically, the iPad Pro is consuming about 1875mAh in total in that particular moment, 1000 of which are coming from the power adapter, and the rest are coming from the battery...

The app reports the maximum current allowed on the Lightning port, as reported by the device. All other Apple devices have reported this accurately. For example, the 6 Plus and the 6S Plus both report 2000 mAh, which is exactly right. All recent iPads report 2400, and older iPads report 2100 (10W).

I hope you don't mind me pointing this out, but it hurts your credibility when your posts seem to indicate that you don't understand current, charge (or capacity), and power ... or their relationships. Granted, apparently the author of the application from which you've attached screenshots doesn't seem to understand it either. (Ah is not a measurement of current.)
 
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Gav2k

macrumors G3
Jul 24, 2009
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Might have to order a lightning to USB c cable and see if the pro will draw more hmm
 

dyt1983

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May 6, 2014
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Might have to order a lightning to USB c cable and see if the pro will draw more hmm

It's always best to find out for yourself but it has been reported here and elsewhere that using the MacBook charger on the iPP doesn't go any faster. Even if the iPP supported a faster charging speed, the way USB-C spec is laid out I am not sure that the existing Lightning implementation would support higher current (because it is USB 2.0).
 
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echo1877

macrumors member
Original poster
Nov 10, 2015
82
107
I hope you don't mind me pointing this out, but it hurts your credibility when your posts seem to indicate that you don't understand current, charge (or capacity), and power ... or their relationships. Granted, apparently the author of the application from which you've attached screenshots doesn't seem to understand it either. (Ah is not a measurement of current.)
Thanks for pointing that out! I assure you I get the difference, that was just sloppy typing. I've corrected the post, hopefully that reads better.
 

Gav2k

macrumors G3
Jul 24, 2009
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It's always best to find out for yourself but it has been reported here and elsewhere that using the MacBook charger on the iPP doesn't go any faster. Even if the iPP supported a faster charging speed, the way USB-C spec is laid out I am not sure that the existing Lightning implementation would support higher current (because it is USB 2.0).
How are people doing doing it tho? USB c to USB to lightning cable? Or as I may try with a USB c to lightning cable!
 

pika2000

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Jun 22, 2007
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Excellent point! Hopefully the lightning port is scalable to support the higher charging rate for future iPads.
 

dyt1983

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May 6, 2014
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Excellent point! Hopefully the lightning port is scalable to support the higher charging rate for future iPads.

Since we don't really know much about Lightning... we'll see. But USB-C supports 60W/100W so I bet we might see that on iDevices. Maybe an iPP will come out in six months with an updated connector (yes people are still bitter about the iPad 4).
 
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tillsbury

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Dec 24, 2007
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How are people doing doing it tho? USB c to USB to lightning cable? Or as I may try with a USB c to lightning cable!

I tried it the other day. Retina MacBook charger with usb-c to usb converter, then iPad pro cable. It wasn't any faster, at least not significantly. By comparison, the retina MacBook charges in no time.

It's a limitation built into the iPad pro, not a function of the charger.
 

masotime

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Jun 24, 2012
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USB-C is the only port that makes sense. I assume that Apple felt it would confuse customers who are used to a lightning port on all iOS devices, but with it comes all the limitations of a lightning port (I mean, charging a device from a female lightning port? what?)

I really hope they switch to USB-C soon, but in the meantime we'll have to "suffer" as first-generation adopters.
 

silverblack

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Nov 27, 2007
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I just charge it overnight and use it during the day. The battery has yet ran out on me during my day. Don't see any problem here.
 
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ZombiePete

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Aug 6, 2008
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I just charge it overnight and use it during the day. The battery has yet ran out on me during my day. Don't see any problem here.
I agree for the most part, however I would hate to be using my iPP for something more intensive and still have the battery drain on me while working. I haven't seen this happen yet personally (I generally keep my screen brightness pretty low, though) but it would be an admittedly weak design choice for a Pro device to have a charging system that can't keep up with its power needs.
 
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Mystro

macrumors 6502
Apr 16, 2011
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Well that was a lot of words....

Nothing out of spec to explain. It's a big battery, it takes longer to charge. That said, my iPad Pro WILL charge while cruising the net with its screen at 50%. I do it all the time.

Hell, I am getting 13 hours of battery life with my Pro with its screen at 45% and location services on while surfing the net. It's not only good but betters any IPad before it by equaling my IPad 3 in battery life.
 
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PBG4 Dude

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Jul 6, 2007
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Is the Amp rating important too for this?
Amps can derived from voltage and wattage. Just manipulate the P = E x I formula to solve for the missing variable. Somehow 12W at 5VDC becomes 2.4A. I think 5VDC x 2.4A = 12W?
 

Gav2k

macrumors G3
Jul 24, 2009
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I tried it the other day. Retina MacBook charger with usb-c to usb converter, then iPad pro cable. It wasn't any faster, at least not significantly. By comparison, the retina MacBook charges in no time.

It's a limitation built into the iPad pro, not a function of the charger.
See you say that it you used a USB c to USB adapter which in turn adds a limitation hence why I've ordered a USB c to lightening cable to cut the dongle out of the loop
 
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