The quality of a lot of USB cables is rather poor when it comes to charging. Using a bad cable you can easily wait 20% longer for your phone to charge. The problem is that there is no obvious way to recognise a bad cable from a good one. They all look the same.
In this video I show how you can easily determine the internal resistance of a USB cable using only a USB power source, like a charger or power bank, a USB tester and LED light as load. I demonstrate the method using the Ruideng UM34C and the UNIT UT658 USB tester.
I reviewed both of these earlier and you can find my reviews here:

UM34C review:    • Review and teardown of the Ruideng U...  
UNIT UT658 review:    • Review and test of the UNIT UT658 US...  

The power bank used in the video is a ASDA Blackweb 2600 mAh and you can find my review and teardown of it here:    • Review and tear down of the ASDA Blac...