usb ammeter and voltmeter
had some fun in the sun yesterday using a solar powered phone charger and usb ammeter and voltmeter to prove that iphones use 800 mA + and thats why they dont charge from most usb ports
http://www.amazon.co.uk/dp/B00JQ5DI4U/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=2LANFWKOV2UNR&coliid=IA6QGWOWZNIA9
https://www.flickr.com/photos/osde-info/14473649914/
also discovered that when the sun went in and the solar power dipped below what the iphone requires that once the iphone detected the dip it never charges again from that port until you unplug and replug the cable androids have no such problem