To maximize charging efficiency, one would want to have 3 battery chargers rather than a single 3 bank.
The three bank is internally regulated to only provide enough amperage to charge the battery at maximum efficiency to maintain battery life. And it only does that to each battery at a time. It doesn't charge all three at once regardless of how awesome a power supply is.
And charging the controller separately is a bonus with the power bank since it will charge from the battery bank only after each battery is charged.
So, single bank chargers will charge faster overall.
