I received the single cell chargers and it would be fairly easy to make a box to house all of them in a neat package with the LEDs showing through small holes in the box. I thought that some 40+ pin connector from a computer could do the trick to connect a 20S battery. But I tried four of them to recharge 4 18650 cells. When all the LEDs were green, checking with my Fluke, I got 4 different voltages from the cells ranging from 4.27 up to 4.35V

So I am disappointed that these little chargers lack the precision that I was looking for. So for now, unless there's an easy way to change something in them to make them cut off at the exact 4.2V mark, I'm stuck with 20 single cell chargers