A5 0.5W is average, atom 3W is max.

Some old Asus netbooks(take R101 model) with 10" screen, harddisk, and 3 cell battery. Its average battery life is around 3.5 hours. 3 cell battery is 23WH, iPad2 battery 25WH. Average battery life is 3.5 vs 10 hours. The old Atom chip max is 6W.  The netbook even has hardisk which consume fair amount of battery. You should be able to roughly figure out the real power consumption of A5. Even exclude the battery size difference, and harddisk factor. The ratio is less than 1:3. Which means A5 is about slightly above 2W.

Intel publishes its max power consumption. No of ARM CPU is not even dare to publish this data.