I just posted a teardown and tests of a $2.50 DIY USB PowerBank Teardown and Tests. Check it out to see what I found.
I recently purchased an Inateck (EC2001L) 120cm USB to Micro B cable that comes with a Lightning adapter for recent Apple iOS devices from Amazon. I picked the cable for its dual-purpose nature, but it is also set apart by its flat profile, which reduces tangles. My plan was to keep it in my bag with a USB powerbank so that I could use the cable to charge the powerbank and iOS devices.
Unfortunately, it isn’t up to the task. First thing I realized is that I missed the fact that it wasn’t Apple MeFi certified. In the past I’ve had trouble with non-MeFi lightning cables leading to slowed charging rates.
The Inateck cable seems to have the same problem. At first I thought it wasn’t allowing the iOS device to properly determine the current delivery capability of the power source, but when I moved the lightning adapter to another Micro B cable, it worked fine, so, the problem must be the resistance of the cable itself.
I did some tests using a multimeter and some USB testing equipment and I found that the cable does, indeed, have high resistance 370 miliOhms or more, leading to a voltage drop of 0.37v at the 1A charging currents used my iPhones, and even more at the 1.5-2A demanded by an iPad. Other cables had less than half the resistance, and correspondingly, less than half the voltage drop.
This cable is fine for data transfer and occasional charging, but it isn’t what you want to use for charging if time or power are precious, because it will take longer than a lower resistance cable.