Having spent over two years reviewing countless types of Power banks, it's a real surprise when I hear people ask "What is a power bank?" or "How does a Power bank work?" The term 'Power bank' is not quite as self explanatory as 'Portable Phone charger' or 'External battery pack.' They are all just different names for the same device. They're basically a way to recharge mobile devices when you're away from a mains power source. If you'd like to learn more about the finer details, I did write a guide which can be found here. Below are some of our hands-on Power Bank reviews. They range from ultra slim lightweight power banks suitable for a single smartphone chargers, all the way up to monster power banks capable of ten or more chargers.