I discovered that not all "standard" USB to USB cords are the same. I needed to charge a small 4.5 volt screwdriver and to increase the amperage I paralleled two USB bluetooth helmet intercom chargers.
For part of my scheme I used two short (6") USB to USB cords that I had lying around. I wondered why the drill was not charging and found that the two short USB to USB did not carry current.
I have other longer USB extension leads which work perfectly so needless to say I modified my charging circuit and all's well now.
Regards, Clive Liddell Pietermaritzburg South Africa