Have you checked your wifi settings-->advanced wifi settings-->keep wifi on during sleep = OFF This setting must be turned to off, else the drain can be really harsh and noticeable. IF it is not that it could be one of those script miners at work that use your hardware when you browse certain websites without your consent to mine cryptocurrencies..If in doubt, clear your browser cache, plugin data etc and use the phone without surfing to test whether something changes. (You could also disable java script in browser and test that way) Regards..
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