How to Make a 50,000 mAh Power Bank from Scrap Laptop Battery

Josif Vissarionovich Batteries are usually spot welded. But you can get
away with soldering but... Soldering iron must be real hot and you must use flux so you can use as little amount of time as possible to avoid damaging the cell. Also your wires are just too thin. They increase internal resistance of the battery. Also if each cell has 2 000mAh at 3.7V then your whole battery has 7 batteries in paralel x 2 000mAh per battery at 3.7V that is 14 000 mAh at 11.1V because you have 3 banks in series wich increases your voltage but not your capacity.

 Wich is another think to consider. Why use so high voltage and then step it down quite a bit? There are regulators which can operate at nominal voltages of the lithium cells and even charge them (no need for BMS board = saved money). Also DC to DC operate at around 80% to 90% efeciancy. Better to loose 20% from 3.7V then 20% from 11.1V. One more thing. I would not trust that BMS board to limit the charging current. Get some proper charger to do that (or use dedicated power bank board that can handle that as well as steping the voltage up / down for that USB, as i wrote earlier).

  Superatition Mountins Very strange decision !!! The wires that you connect are too thin. The battery protection module for the wires is too powerful. It should increase the cross-section of the wire at least to 0.75 mm, then the assembly will be quartic! You did not measure the capacity of the batteries, if it is different, your wires and batteries will burn.

  Matthew Miller Why would you use a 3S pack to get 5V output? It would make so much more sense and simplicity to have a 1S pack and use an off the shelf buck-boost converter designed to run a phone charger controller PLUS you wouldn't need a proprietary charging adapter, you could charge it with a USB cable.

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