Why is Android System draining so much battery?

[carlosbelloc]

Recently my Galaxy S5 has been draining battery extremely fast and when I go on to Settings and Battery I notice that Android System is almost using twice the power that my display. This happens even when it is not in use and I have left the phone overnight with 100% and wake up in the morning with 35% or even less. I have uninstalled many apps that might consume power and lowered the brightness on the display but none seem to make much difference. What can the problem be?