[erikpukinskis]

I am not any kind of battery engineer, but...

My understanding is a primary limitation for these batteries is cooling. Cooling ability is relative to the surface area of the battery. One giant battery has much lower surface area than a bunch of small ones.

Also having a large number of batteries lets you put different cells on different recharge cycles to maximize battery life. You can use a small number of worn out cells for brief minute-to-minute fluctuations while you keep fresher cells on longer cycle that optimizes lifetime. With one big battery you're just stuck with whatever wear characteristics the usage curve gives you.