@techero I tested out the theory I had suggested, the effect on battery drain was minimal if any, but the CPU utilization did not spike after turning off the screen. It also had at least had one positive side effect in the form that earlier I used to miss calls since my phone would take several rings from the caller before it actually rang on my end, now the ringtone plays(on my end) on the first ring(at caller's end), so I don't miss calls as a result.

I am now testing out the effect of toggling Wifi and can already see the battery sustain its level longer with Wifi off even with a SIM card, so now I can at least use the phone for calls and SMS quite reliably(had tested this before too thus confident).

My phone's dmesg shows that it keeps trying to start and kill two services 'imsdatadaemon' and 'imscmservice' every three to five seconds(irrespective of the Wifi status) so looking further into this as well.

PS: This is based on my experience on Development channel Version 531 on Redmi 4X. The battery was recently replaced(unauthorized) so this also can likely be one confounding factor and my experience may not be indicative of other's experience.

@pglushkov I am not an expert in any way, but I have been facing the same problem myself based on a hunch I would say try to change your sleep settings under Battery to Never and see if that helps. I am testing it out myself and at least one thing it does based on what htop and top say is that if I set the sleep to Never and then turn off the phone's screen by pressing on the power button the CPU utilization does not go up. There is another thread on High CPU usage and I think perhaps the root cause is the same. Let me know if it works for you, in the meantime I am trying it out myself will update in a day or two if this helps with battery life at all.