Here is an excellent article about charging android phones
Android USB Charging Secrets - APC
I purchased a tester and found that chargers, cables and USB ports all change the amperage that goes intot he phone. As well there is a signal that goes over the data portion of the cable.
Here are some of my findings:
1) cable wire is a big deal. 28/24 is the best (heaviest gauge). The ones you buy in the gas stations and Walgreen's are thinner and may not allow the power needed for faster charging
2) two identical HTC M9 chargers (longer body) One charged at 1.05 ma and the other at .95 ma. same outlet. Phone (HTC One M9) stated "(AC) charging"
3) EverReady Energizer 2 AA batteries phone stated "(AC) charging" @ .43 ma
4) Fully charged 2400 ma rechargeable charger w/ cheap short cable would not charge for more that 3 minutes phone stated (USB) charging. Message = "phone using too much power cannot charge"
5) Fully charged 2400 ma rechargeable charger w/ good cable = "(AC) charging" @ .25 ma
6) Best results! USB 3 computer port. "(AC) charging" @ 1.45 ma
7) Cigarette car charger w/ good cable (USB) charging" @ .45 ma
8) Car USB port w/ good charger (USB) charging @ .95 ma
There is a handshake between phone and charger and it depends on the cable data port voltage and message that controls amperage. Some phone and charger manufacturers ahve set up proprietary handshakes to get faster charging!