Recharging devices with big battery via USB port on your PC or Mac may be frustrating, because USB ports got low power and it takes ages to recharge devices like big iPad Pro. USB ports were not created as replacement of other charging methods, it’s just additional feature, not main feature, but I enjoy to have connected devices to USB port without taking care of battery, because “incoming energy” from USB port is still higher than “outcoming energy” from device I use – until I use really power hungry device, like big iPad Pro with brightness set to maximum.
12.9-inch iPad Pro got as first iOS device feature called Quick Charge, which allows you to recharge your iPad battery from zero to 100% more than 2x faster. Of course, it won’t work with charging via USB port – it will be still about 10 hours. But included iPad Pro charger from Apple is only 12 W and it takes about 4.5 hours to recharge it from zero, so if you want to benefit from Quick Charge feature, you have to purchase 29 W Charger and USB-C to Lightning cable certified by Apple, which are quite expensive, but if you have ultraportable MacBook Retina, you already got it – charger and cable are the same. But some users refer, especially on iOS 10, that iPad Pro is discharging when on 29 W charger! What is it? How to fix it?
No worries, in most causes it’s not hardware failure, it’s just software bug. I don’t know why is this happening, but if you are charging iPad Pro and % are lower and lower, try hard reset – hold power off button and Home Button at the same time. You may need to do it 2 or 3 times, but after this, battery % will be shown correctly. Just take note: do not use this combo while connected to Mac or PC with iTunes – it will turn your iPad (as other iOS devices) into service mode and you will need to reinstal your iPad from scratch or from the latest backup.
Second way is just to left iPad Pro charging. You may experience some battery’s %s drops, for example from 95% to 87%, but after some time, it will fix it by itself.
This is a strange bug, and if previous hints did not help, it may be hardware failure. As for me, I have never experienced this battery issue when my battery level was under 80% when I began charging. And when I tried to recharge my iPad Pro via USB port in my iMac, I have never experienced this issue too. So before going to authorised service, try to use another methods – USB port or included 12 W charger – to make sure it’s just software issue.
Update 1st – 03. June 2018: similar issue is with newer versions of iOS 11 and 29 W charger combo on iPad Pro. As for me, charging sometimes stops at 96% and then battery’s %s are dropping down. Solution is simple: eject power cable from iPad Pro and then restart it. Then continue to charge battery as before. It solved this issue I’m experiencing.