[hamandcheese]

For that matter, why not have 7x the batteries at 1/7 the capacity? Or does the charge rate not depend on the capacity?

[hwillis]

Charge rate is independent of capacity. A 3 C battery charges in 20 minutes, whether it's 1 kWh or 7 kWh. If you have 7 batteries, each charges in 20 minutes.