Just a very basic test this morning. I only used Ampere to monitor so that I could see mAh in the notification panel but I didn't use an app to actually graph the charging cycle.
Test done with included fast charger that comes with the phone.
Other than not using the phone, I didn't change anything. I was still getting email, text, Twitter notifications, WhatsApp messages, etc. Second screen was on. The only time I touched the phone was to quickly bring up the lock screen so I could see the charge percentage.
I started at 28% and the first interval was to 53%. That took 15 minutes. So for that interval the phone charged at 1.67%/min (25% divided by 15 minutes). Ampere showed 2800 mAh, which is much faster than the max of 2100 that I ever saw on the G4.
Next interval was 53% to 71% which took 14 minutes and the charge rate was 1.29%/min during that interval. When I checked this time, Ampere showed 2100 mAh.
I think I remember reading that fast charging is from 0-60% so that would explain the drop off in charging current.
I ended up letting the phone charged for exactly 60 minutes and ended at 95%. So the phone charged 67% in 60 minutes to give an overall charge rate of 1.12%.
It should be noted that after 90%, the phone enters trickle charge and only charges at about 1% every 2 minutes.
Fast charging is designed to top off the phone in a short amount of time and although 1.67%/min may not be the fastest charge rate for a phone, it certainly gets the job done, especially when you consider that the battery could just be swapped for a full one.
For reference, the fastest charge rate I ever saw my G4 do was 1.2%/min.