The soldering is the tricky part.
If you solder too long, the magnets lose their strength (see FAQ
But you'll get it with a little practice.
As you can see in the picture, they still have enough strength to hold three batteries.
By the way: The measured electric resistance of such a charging cable (positive and negative cable) is below 2x 0,025 ohm.
Note from the supermagnete team: Another option for charging batteries shows the application Universal connection for battery charging device