Thrunite C2 External charger problem

I'm having problems with my new 2018 Thrunite C2 external charger. I bought three of these as stocking stuffers for Christmas, but as they stand I question If I can actually hand them out as gifts.

More often then not, the charger stops charging my iphone5 (with 2 week old new integral battery) after only 15 seconds of charging. It's very frustrating. It might go from 19% charged on phone to 20% charged and then the charger stops charging all together.

Any ideas what might be going on? Could it be that the Iphone5 draws so little power that the charger has a hard time recognizing it? I'm baffled as to what might be going wrong here... any help much appreciated before I RMA all three.

I've had similar problems with the C2. It turns off on some loads and this has nothing to do with the relatively high minimum shutdown current of the early units. It's not a very reliable powerbank.

What other charger is out there with single 18650 removable cell?