For the first months since I purchase the 5s, the battery life was terrible, I've read over the net that the 3-4 hours that I got from 100%, was possible with few degrading variables such as heat, low signal strength , higher brightness, etc. Luckily my original USB charger died, possibly from overheating after plugging the phone 8 hours a day to it at work , while using the phone extensively, browsing, gaming etc. Then I used my brother's USB charger. I noticed the charger stays cool all the time, and the charging output was low, took me about 2 hours to get to 100% from 0%. Unlike the original that got me to that with 30 minor less. The day after the battery life expanded amazingly, doubled and even more, right now I'm at 7hours and 5 min of browsing, and messaging with 30 min of gaming, and at 18 % left. I remember reading something that slow charge expands the battery life, in comparison to fast charge. If this does not damage the phone,(which I think not because it's USB charger with same lightning connector) then I can't see myself charging with the original ever again.