[Dr. Iguana’s] experience moving from jobs powered by disposable Alkaline cells as well as linear regulators to recycled Lithium Ion cells using the buck regulators seen above may serve as an motivation to make the shift in your own projects.
The recycled cells he’s speaking about are pulled out of larger battery packs. As we’ve seen in the past, dead battery packs for rechargeable tools, laptops, etc., are frequently plagued by a few poor apples. A little number of dead cells can bork the entire battery even though numerous perfectly usable cells remain. when he chose to make the switch it was time to think about power regulation. He very first looked at whether to utilize the cells in parallel or series. Parallel are simpler to charge, however increasing the voltage to the preferred level ends up costing more. He chose to choose cells in series, which can be regulated with the a less costly buck converter. In this situation he made a board for the RT8289 chip. The drawback of this technique needs that you screen each cell individually during charging to guarantee you don’t have the exact same issue that killed the battery from which you pulled these great cells.