A friend had one of these batteries on his Samsung S4. It had great battery life, double the standard one. But the downsides, the back cover to hold the battery is bad quality and very bendy, the phone is almost twice as thick, the pouch it comes with is crappy , and it's impossible to find a good protective cover. Plus the phone is heavier and even dropping the phone a short distance onto a desk for example, the cover comes off and the battery falls out. For me it takes away the whole attractive look and feel of the phone, and it's easier just to carry a spare battery, having this ugly thing stuck on the back of your phone isn't worth it.