How much additional usage time from the HyperJuice battery for MacBook?

Users can use the following calculation to find out the approximate additional usage time from HyperJuice battery.

For example, the MacBook Pro 13" (mid 2010) which has a 63.5Wh rated internal battery which Apple claims can last for up to 10 hours.

With the HyperJuice 222Wh battery, the calculation will be 222Wh / 63.5Wh x 10 hours = 35 additional hours which gives a total usage time 45 hours (from using both internal and external battery).