Also, and this is entirely speculation and I'd love to hear a battery engineer confirm this, but: if you're packaging together cylindrical batteries, it inheren

Also, and this is entirely speculation and I'd love to hear a battery engineer confirm this, but: if you're packaging together cylindrical batteries, it inherently gives you more air channels between the batteries to promote cooling. When you're talking tens of kilowatts, both in discharge and charge rates, the percentage that ends up as waste heat suddenly becomes a whole lot of heat. You probably wouldn't want a maximally stuffed cavity with these packs turning into a single, massive chunk of thermal mass. EDIT: looks like I was firsted somewhere below, doh!