[MetalMan]

For car guys it is a lot easier to work with. Generally the cheap end to end "shotgun" packs for RC cars are connected together by thin nickel strips that can't handle a high amp load, and so get really hot when they are pushed. Airplane guys solder their cells end to end, which will create a much lower resistance than side by side, but once they get the cells together like this, there is no getting them apart. And that is why we tend to use side by side.