Battery draining after 6 hours?! Samsung Galaxy S4mini

[AC Question]

So I got Samsung Galaxy S4mini 6-7 months ago. Everything was amazing until I accindently updated my phone to Android 4.4.2 KitKat . First few days it was a nightmare! The phone was blocking non-stop. After a week things were getting better. Now it doesn't block at all .BUT my battery life is awful! If I want my battery to survive at least 6 hours the phone needs to be in airplane mode with the lowest lightnes. And it has been like this for 2 months !
I did everything to extend battery life but nothing seems to be helping.
I have maby 5 apps ( other than the default ones) .
And now I am looking at the usage percents :
Android OS - 84% ?!
Screen-7%
Waiting- 4%
Android system - 2%
Innaction- 2%

How can I extend battery life? What and why is android os using so much battery?

PS. Sorry my english is bad :/

 

[Rukbat]

Android System and OS use a large percentage of the battery, but around 25%, not 86%. It sounds like a bad update to the kernel. If it were mine, I'd bring it to the carrier and ask them if they could reflash the update for me.