Charging 20v battery without charger why this works in description

What I’m holding when I say, “self explanatory “ is, two wires that are exposed on each end. (Jumper wires). The red wire that connects the two wires is there to keep + from touching -. That little 2” red wire is for safety. I mention this later in the video.


Leave everything unplugged, until you’ve made all connections. I’ve been charging my batteries this way for years. Works great.
And for those that do not know why there are more than two terminals on battery chargers,and drill batteries, also why drill battery chargers will not produce any voltage while testing with a voltage meter..
It ALL has to do with TEMPERATURE sensors in the batteries. That’s why this way works. When I place the main battery on the charger, the center terminal, as a temperature sensor, will tell the charger,
IM NOT TOO HOT, nor TOO COLD. YOUR OK TO SEND
THE CURRENT TO THIS BATTERY.
If you want to know more about this, google: LITHIUM BATTERIES AND EXTREME TEMPERATURES WINTER SUMMER.
Update

There is a chance of over charging the secondary battery , or piggy back battery…I have found with these dewalt chargers, the dewalt battery on the charger stops the charging process for both batteries. So for best results, be sure the dewalt battery is not as depleted as the piggy back battery. And do you can’t expect the secondary to charge fully. I don’t recommend charging two dewalt batteries with the same piggy back battery.