I tried to make a powerbank, i used a lithium ion battery (Panasonic NCR18650B 3.7V). I increased to 5.10v with mt3608 dc step up (https://www.addicore.com/MT3608-Boost-Converter-p/ad300.htm) I give 2v 2v to usb data pins but in 10 minutes, my iphone's charge is from 57% to 60%. Otherwise with my powerbank it takes 3 minutes. My diy powerbank is very slow why it is like that?