Now before everyone start saying how bad or dangerous it is to connect used and new 18650 Li-Ion Cells together - I would like to keep it technical and fact based.
I (like many others) have many used cells ling around and would like to be able to utilize them the best way possible on high current / voltage device (scooter / e-bike etc).
Connecting in series is clearly a bad idea as when one cell voltage drops below the lower limit it will 'permanent damage' point.
Now in parallel (assuming I pre-charged them to a similar voltage ) - what would really happen?
Used batteries will have less capacitance and their voltage will drop more rapidly but they can't because they are connected in parallel so defectively what I would expect is that "each cell will supply whatever current it can" until they all drop together to the minimal voltage allowed (where I would stop the discharge) . I will connect 5, 10, 20 cells in parallel and use a DC2DC Step up to convert them to the needed voltage.
The only thing I can think off is if the internal parallel resistance of one cell is reduced over time - self discharging and leading all other cells to discharge through it. I really want to find a way to maximize my scooter and use so many old yet good cells (ranging from 1200 to 2200mAH left in them).