The "jelly roll" is just one packing technique. You can pack flat sheets, so in theory can create an L shape. Another guess is with an L shaped battery, therma

The "jelly roll" is just one packing technique. You can pack flat sheets, so in theory can create an L shape. Another guess is with an L shaped battery, thermal expansion makes it tricky because the L shaped compartment has a sharp inner corner which runs this risk of stressing the battery when it expands. A square compartment does not have that issue. In any event, Apple knows how to produce weird shaped batteries. Just look at the Macbook. But it's in a nicely shape space.