Who I have the same questioned this topic

Before lollipop 5.0 my battery lasted all day. After the update it lasted about 3 hours. It stabilized for a while then the security patch happened and it went back to lasting 3-4 hours. I noticed there was an update yesterday, but STILL not the update lollipop 5.1.1. I don't understand why you can't update the S5 to the most current OS especially when other Samsung products have been.
And all of my apps are currently updated. Yesterday was the first time in I don't even know how long that the charge lasted 8+hours. But then the security patch happened and it's sitting on the charger after 4 hours of LIGHT use.