Bests & Worsts Reviews from Amazon

As an engineer I test every battery I own so, naturally, I couldn't wait to put this one through its paces. It has some positive qualities but they're completely overwhelmed by the lousy capacity. First the good: * Using both micro-USB inputs (provided each is coming from a capable supply) really does charge this battery quickly. Two 10W chargers brought it to full in under 8 hours. * Each output will deliver over 2A, even simultaneously. Understandably the battery gets warm when you do that. * It makes a great charging distribution center. My family, with four phones, three iPads, ereaders, headphones and various other devices, took it on vacation and instead of having to hunt for wall outlets (leaving things plugged into random places in the hotel room) we used a good 10W charger to power this and, overnight, it charged everything else. In the morning our gadgets would be full, this would be around 50% and while we were out it would come back to 100%, ready for the next night's work. A multi-headed charge cable makes it even better. * It's heavy but that's in the "good" column because it's not as heavy as I was expecting. I had it in my backpack for a while and didn't notice the extra weight. Of course that's probably because of the severe downside... And that downside is: * Delivered capacity is only about 70% of the 20000mAh stated. I've charged this battery to full and run it down completely with a good power meter and got consistent results of 13739mAh, 13703mAh, 13828mAh. Originally I gave it two stars but see the update for more detail. UPDATE As others have pointed out the 20000mAh rating is the raw capacity of the 3.7V cells. Some level of efficiency loss is guaranteed (thanks physics!) but reporting the capacity at 3.7V for a device that delivers 5V seems shady, at best. Unfortunately it seems to be the industry trend so I don't think it's fair to penalize EasyAcc - I've added two stars for that and the fact that I find myself using this battery, especially on vacations. Recently in Disney World, for example I had this and a rats nest of wires in a small backpack and I was able to keep all four phones charged until the park closed, despite the battery-hungry games we played while waiting in lines. Even with snacks, a sweatshirt, random souvenirs and a spare phone in the bag (because one of us has a habit of taking a phone swimming) I hardly noticed the weight.