The capacity of these power banks are specified at the nominal Lithium Ion battery voltage of 3.7 volts. So 20,100 mAh will be at 3.7V, not at 5V. To work out what it will be at 5V, divide them. So (3.7/5) * 20,100 = about 14,874 mAh at 5V. Then the charging and voltage conversion circuitry are each about 90% efficient. So take 90% of 14,874 and you get 0.9*14874 = 13,386.6 mAh available to power the PAW at 5V. The PAW draws an average of about 0.7A at 5V, so theoretically you can eek about 19 hours out of said power bank.
In my testing experience, you get somewhere between 17 and 18 hours from an Anker 20,100 mAh power bank.
I would expect a 10,000mAh unit to get about half that, 8-9 hours.