try this:
PART 2 - BATTERY LIFE IMPROVEMENTS
I noticed that the helio x20 is quite the power hungry chip so I dug around XDA MIUI devices forums for other devices and found out that Xiaomi MIUI roms use a service called 'perfservice' to control the CPU and can sometime be a hit and miss, so I did something;
DISABLE PERFSERVICE and MY BATTERY LIFE HAS IMPROVED DRAMATICALLY. IM TALKING REDMI NOTE 3 SNAPDRAGON LEVELS. 7 HOURS SCREEN ON TIME, 20 HOURS STANDBY.
What happens when perfservice is disabled is the cpu is controlled by MTK's cpu manager (not sure what it is called) and uses the stock interactive governer (which is good).
HOW TO DISABLE/IMPROVE BATTERY
1. Make sure you are rooted
2. use your root file explorer of choice (I prefer fx file manager)
3. go to /system and backup build.prop by copying and pasting it somewhere else
4. edit build.prop and find the line ro.mtk_perfservice_support=1 and change it to ro.mtk_perfservice_support=0 and save file
5. go to /system/etC and find a file named perfservapplist.txt and rename it to perfservapplist.txt.bak
6. go to /system/etc and find a file named perfservscntbl.txt and rename it to perfservscntbl.txt.bak
7. Reboot and test out the result yourself
I got this from
redmi note 4 xda forum (i cant post links)