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I've had this issue a couple of months ago too but then I could fix it by turning off an option at my WiFi settings.
Now the problem is back but it my previous solution doesn't work.
I own a Samsung Galaxy S5 and I've had it for about a year now. It runs on Android 4.4.2. At some point the battery started to die really fast, and I don't have a clue what the reason could be. When I check the battery usage, it says "Android-System" uses about 30-40% of my battery, but I don't have a clue where this service comes from or how to kill it.
Has anybody got a solution for this?