normal 120V receptacles are 1500W max, so that's about all you can charge from.
Then there's batteries and how much they'll accept. You can't just charge as fast as you want. The datasheet lists a C-rate for charge and discharge. Stay at or under that value.
example:
Your batteries are 2C charge rated.
You are running 40Ah batteries, 24 in series. 2C would be 80A at 72V which is about 5760W. Your normal 120V receptacle is right around 1500W, so you can really only get a charger that does 1500W or below, unless you choose to ONLY charge with 240V, then you could get a 240V 30A receptacle and a 5000W charger and you should be able to charge in 30 minutes.
This all decreases the life of the cells though, the faster you charge or discharge the worse it is for life.