Reliable wireless Battery charging
The technology you may looking for is 'QI wireless charging'. 

There are covers like LingsFire® 2 in 1 Qi Wireless Cover (German link) using that technology and there are other approaches like LEAPCOVER Universal-QI Wireless Receiver Patch (German link as well) where you can actually fit it into your iPhone. 

I found a link for you addressing that: www.forbes.com/sites/ewanspence/2014/12/11/qi-wireless-charger-iphone-6/#2d1685987fb2

You may also do a Google search with the keywords 'qi' and 'iphone'.