https://www.amazon.com/dp/B00J3JSEG6
I just bought it, used it, and love it.
do you have or can you get a USB volt/amp meter (something like this - www.amazon.com/dp/B00J3JSEG6)? it will show if there phone is actually drawing any current from the charger.
if not - it's showing 0.00 amp flow - then things that could be wrong are....
1) battery could be bad
2) battery may not be properly/fully connected
3) bad USB lightning cable
4) charging circuitry on the motherboard may be damaged
as it's an 8, you could also put the USB meter between the wireless (Qi) charger (if you have one) and the A/C adapter and see if the it's drawing power that way too. if not, that could indicate the Qi flex coil is damaged or not connected to the motherboard properly
Current is what really matters. If your device is only drawing 1.5A and not 3A, the resistance value is kind of academic. Using a USB ammeter would be much easier than all of this. Something like this:
http://www.amazon.com/DROK-Multimeter-Capacity-Charging-Alignment/dp/B00J3JSEG6/
I have no experience with this particular one but they are not uncommon or expensive.
I got this one - the cheaper LED display version.