I guess ebikes are pretty pathetic, compared to a 50cc moped. Multiply the Ah rating of a battery by its nominal voltage to compute watt-hour. A 36V10Ah pack is 360 watt-hr. A 48V13Ah pack is 624 watt-hr. Higher voltage gets you more watt-hr.
At 20 mph, you probably use 20-25 watt-hr/mile if you don't pedal. Those two packs are in theory good for 15-18 miles and 25-30 mikes at that speed. I'm not sure they will do that well. The battery wears out with that kind of load. If yu're willing to add some assist and go slower, range can be go up.
Here's the ebikeling thread.
https://www.bikeforums.net/electric-...g-36v-kit.html