Redmi Note 4 has a software bug which prevents CPU going to deep sleep. This is easily observed via CPU Spy or some other similar tool.
There are couple of ways to solve it, but the easiest one is just to swap your SIM card to one that supports LTE (4G). You don't have to use 4G networks, you just need new SIM card and CPU will go to deep sleep.
If this is not option for you, this is permanent solution (requires root):
http: // en .miui. com/thread-386101-1-1.html
Also there is temporary fix (which works until phone is restarted), but I just can't find it anymore
Try googling turn on "lte ram dump deep sleep" or something like that. There is step-by-step manual how to enable deep sleep from hidden service menu.