mobile

I was getting awful battery drain whilst screen was off, realised that whilst wifi is on, the tablet never ever deep sleeps. literally 0 seconds. of course with it turned off it does deep sleep. and within 8 hours 0% of battery is lost.

Is there a way to fix this issue?
Secondly, on wakelock detector, nothing is detected under kernel wakelocks. how come? it;s been more than 20 hours and still nothing.

any help would be great.