It seems like I have done it in the past, but for some reason when I hook the clamps of my 12 volt battery charger to the correct parts of my cigarette lighter plug, that is my cell phone charger, the cell phone will not charge. The cigarette lighter plug lights as if it is getting proper power, and the phone recognizes the power but displays “unable to charge” WTH???
Not an expert here but I think the output from a charger for a 12v battery is not the same as the output from a 12v battery and your phone is probably sophisticated enough to tell the difference. Unless you have the clips switched 
This has happened to me. Usually the tip of the cig lighter plug adapter where it plugs into the phone is not making good contact. Replacing the lighter plug solved the problem.
Plug is good - it works in the car. I misplaced my home charger so I just attached my car battery charger to the plug. The car battery charger wors great to power other 12 volt DC stuff. It measures about the same as a cars voltage when the car is running, about 14 volts.
I have often wondered how “clean” the power is from a charger for use in powering stuff - I guess the phone is too sensitive for the AC to DC charger/power supply.