Trying to make a little powerpack for my boat with old 18650 cells. I am planning on a 1 kWh pack, so charging each cell individually is not an option...
I have planned to set up 10 packs of 4 parallel, and 3 in series giving a nominal voltage around 12 V (this setup makes it easier to check for bad cells for my use). Since the cells are used the need for a protection device is critical.
To charge these packs I need a very very cheap solution.
Solution 1 is to use cheap TP4056 with a battery protection such as this one, 5V Micro USB 1A 18650 Lithium Battery Charging Board Charger Module+Protection for 1 USD a piece and set three of these up for each pack. This module has an builtin battery protection device, a MOSFET ML8205A (I have no idea what this is, but it has high power and current handling capability).
Solution 2: Use cheap 3S basic balance chargers (I have seen these for as low as 3 USD) and get some device to cut the power when under critical charge for each set of parallel.