Benefits of square vs. triangular/hexagonal packing of cylindrical battery cells
In addition to Marcus Müller's suggestions, consider that battery packs often end up as rectilinear prisms.  So take different stacking arrangements of finite numbers of cells (3, 4, 5, 6), stack them "square" and stack them "triangular", then calculate the area of the smallest enclosing rectangle.

Somewhere on the Internet there will be a guide, but for any number of circles, there's a crossover point between triangular stacking and square stacking being the most efficient use of space for finite numbers of cylinders.