I'd heard that these chargers were the most powerful. Opted to buy the middle size/power model as wanted to be able to carry it in my handbag easily but with maximum power. It's done two full charges and no power loss from the unit. Think I should've gone for the smaller one based on the size/weight but am happy. Really good product. I do think that the charged that you have to buy separately should be included though. Fortunately I'd read the reviews before buying and ordered at the same time.