I got my Sony Xperia Z2 2 days ago, when I turned it on for the first time it was on 50% I used it a little then I charged it to 100%. I went to power managment and it showed me 24 days in standby moze with Stamina Moze, the battery life was excellent but once I charged it again the battery wasn't the same before. It showed me 5 days in standby mode and only 10 hours of usage. I'm using the Stamina mode and the brightness is put to the lowest. How can I bring back the battery life like it was at the.beginning?