Designing a parallel, rechargeable circuit out of 18650s
Li-Ion rules:


You mean Series! Series, to increase the voltage
Parallel is absolutely ideal, since there is no balancing required, since they are parallel, they basically share the same voltage
Do NOT EVER permanently add a resistor to the batteries! This over time will discharche them and yield in a fire hazard
if you have no idea, how to make that circuit, do not make it please. I know, that is the typical answer, but the understanding of the principles is mandatory for working with high power batteries, which can set fire to anything if done improperly.
To connect them in series you will need a balancer capable of:


Under voltage detection and cut off
Over voltage detection and cut off
Balancing the load (either pump the power from cell X to cell Y or at least limit the voltage of each cell by discharging to precisely 4.2000V max (It never should go over that for even a second. At 4.3V the Cell gets basically destroyed in an unpredictable manner)! Rather use 4.05V as the "fully" charged voltage. You barely loose any capacity, but realy improofe safety my an order of... no idea, but it is much much safer and gives room for errors - that is the main reason. Also storing a battery at 100% charge will shorten its life and results in a slight fire hazard again.



My tip for you: If you want a power bank, just parallel them up and boost the voltage afterwards. This is 100 times more simple to implement and increases safety a ton.
The only problem with parallel cells: If one is damaged and self discharges, it will discharge every other cell. So make sure, this never can happen. Each discharged cell is a hazard, especially when getting recharged.

Have fun. And never exceed 1C charging (better 0.5C) and the rated C discharging current. Than you should have fun. I also reuse old 18650 cells. But store them in a steel container for safety (plastic layer, to prevent shorts etc...)