I have the lumia 920, The otterbox - and a random wireless charger from ebay.
It DOES NOT charge with the otterbox on, the distance is too great.
This shows, not only the receiver (the lumia) but also the sender (the charger-station) has to be built to a certain standard.
This is simple "induction" - and if the transmitter is too weak, well - then it is too weak to bridge the distance.
The otterbox has unnecessary thick material exactly on the spot where the coil and the camera lense is, this
means it is a matter of luck whether the charging will work, or no - probably the original wireless charger as sold by nokia
will do just fine (nokia usually goes with the better quality) - But if you buy some other QI charger .. you may not be so lucky.
best regards from finland
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N8,N9,Lumia 920 ...to me, the iphone is dead since its birth, but then again.. i am a quick learner.