Many USB battery chargers will state it as 5000 mAh or 20100 mAh. Some of these batteries can charge a Macbook 12 inch notebook. On the other hand, Macbook 12 inch battery capacity is stated as
Built-in 41.4-watt-hour lithium-polymer battery
How can this mAh be converted into watt-hour: or, if the battery capacity is 20100 mAh, then how many times can it charge the Macbook for?