The best thing you could do with these cells is to use them in low wattage applications.
You can create some DIY garden lights. Connect a led strip to a couple of paralleled cells and hook them up to a cheap solar panel.
One trick I learned is to bottom balance the cells.
Its less important when all the cells are topped up than it is to know that all the cells run out at the same time. (for series arrangements)
heck use the first 12 P (approx 15-16 ah) and make your own uber power bank to learn and abuse (does not matter what happens to them).
To charge just run (2 wires) 1 each with a wire with two magnets from you regular charger to the battery bank (one +, one-) and let it treat it like a giant 18650 cell.
What happens if one cell get a to 4.2 volts and others are at 3.9? Does it stop charging?
Or 3 are at 4.2 and one at 3.9 will the other 3 over heat and be dangerous?
If the cells are in parrarell and there are two cells with same capacity but significant internal resistance difference (IR for short -say, 50 mOhm and 450 mOhm), while unloaded, voltages are equal. In the moment a current is forced into the cell, in first seconds most of the current flows through the lower resistance one. However, since it means that 50 mOhm cell is being charged faster, its voltage increase quicker , while on 500 mOhm it is going up more slowly.
Let’s say both batteries are at 3,2V and then 1A current charging starts. at the beginning, the resistance is 9 times greater on 450 mOhm, so there is only 0,1A, while 50 mOhm gets 0,9A. So the batteries resist actively with 3,2V + passive IR.
After a while 50 mOhm one got more charge, so its no-load voltage increased to 3,25V, while 450 one got less charge and have only 3,22V. Thus, the charging current flows 0,84A through 50 mOhm and 0,16A through 450 mOhm cell. When the voltage difference reaches 0,4V, the current equalizes on both batteries.
Now, when charging goes into CV stage, with 4,2V the 50 mOhm cell is topping up quickly (it has over 4,17V of no-load voltage(, while 450 mOhm still has 3,8V, so current on 50 mOhm quickly decreases while current on 450 mOhm is fading slowly. Since the cutoff should happen at charge current/10 the 50 will be a little overcharged and 450 a little undercharged. After cutoff, the voltages on batteries are not equal, so the 50 will charge 450 a little, until voltage equalizes.
The bad thing is - that at the start ‘better’ cell gets practically full current charge, so if we have to charge cell with 0.5A, for a while better cell is charged with too high curent.
Balancing is not really an issue if you use a BMS with balancing and/or a few balance boards, affordable stuff in AliExpress.
If you can live with a little bit more losses you can use independent 1S BMSes per stage. By using a multi-pole switch you can route each stage anode(s) to each B/P+ BMS input, in such a way that when the switch is off (all BMSes powered down) all of the MOSFETs disconnect and the series P-/anode links are disengaged. Additionally, if we bridge all of the switch pins for the “off” position (all anodes connected) we would just need to bridge the cathodes for a self-balancing full parallel setup, doable, for example, with a multi-pole 5V relay (or more). Now add some TP4056 boards and you can even charge via multiple in parallel phone/tablet chargers.
