Hopefully someone knowledgeable can elucidate properly but I believe cylinders are an inherently good shape for certain types of battery. The internal chemical process relies on two surfaces being in contact. You can roll up two surfaces and put them inside a cylinder which gives you lots of contact surface area in a small volume.
And a space in between to cool them. Charging and discharging a battery goes through Ri (the internal resistance of the battery) and as a result they get warm or even hot if not adequately cooled.
