iPhone charging issues from bike power source

As title suggests. I've not used my phone much on the bike mount so not needed to plug it in but today I set off on a journey with around 6% life in the battery, used my sat nav app then the power gently dropped till it all stopped working. I use an iPhone 6, addons case, 12v (fag) power take off socket, a Usb plug and a spurious well made lead.
Has anyone had similar problems on their bikes with bike charging systems?
I think the power source fluctuates therefore the software in the phone refuses to accept a charge. My volt reading is 14.6 during riding as I've a volt meter fitted.
I'm going to try it in my van in the next few days as all the components seem to actually work separate.
Anyone to shed any light on the matter?

 

Think I've sussed it. Plugged same charger/lead/phone combination into my van this morning and hey presto all fully working. I can only think bike is overcharging when running, software say too many volts to damage and shuts down. When I stopped yesterday to fix it the only time it took a charge was when the engine was off. I did notice a few flashes of life but not if I left engine running.

 

Looks a nice bit of kit but it's not what the bike in question needs although might get one for my others.