For each paralleled group, there are twenty cells. I arranged them in 2 by 5 groups and paralleled each two groups of cells further together. In my opinion, this is a little easier to work with given the smaller size of each group. The cells within each group are welded together using 8mm nickel strips. If you are interested in making a spot welder yourself, you can check out my earlier post on how to make one.

Ideally, each cell should be separated using plastic cell spacers. Besides providing structural support, spacers also allow airflow among cells. This is helpful for heat dissipation and is crucial if Li-ion batteries are used, as thermal runaway can become a fire hazard. Li-ion batteries heat up when they are grossly over charged or discharged at higher than maximum specified current.