I found a new great battery pack project on instructables by DIY KING 00
and he has been working on motorising his bicycle using a geared DC motor. For that he needs a battery pack. So to make a battery pack he have decided to go with the popular 18650 lithium ion cells from two old hoverboard batteries. Since the cells are from used batteries, he need to balance charge all the cells before making the battery pack. Everytime he use these 18650 cells he need to go through this stage when he needs to balance charge all the cells individually to get them at the same potential.
To get through efficiently he decided to built a dedicated charger for 18650 cells. He also decided to make it a modular charger so that we could add up modules to form a larger grid that enables us to charge as many cells as we want simultaneously.