Based on the information provided, we can calculate the time required for charging. If the power of the charger is 66 watts and the battery capacity is 20,000 mah, we can calculate the charge time using the following formula: Charge time (hours) = battery capacity (mah)\/charger power (watts). So, charging time = 20,000 mah \/ 66 Watts = about 303.03 hours. As a result, charging 20,000 mah takes about 303 hours.