Hi,
Would like advice on this really weird problem…

My phone lately started shutting down when the battery reaches about 20%
When I start it back up the battery starts draining really fast, in 2 seconds 5% gone, and then shuts down again before reaching 0 (or even 1).

It does so until I start charging it and only then the phenomenon will stop.

Today it reached a really ridiculous level, that it started doing this in 37% .

I tried scanning in 2 different anti virus and the malewarebyte but nothing came out and I didn’t download any new app before this started.
It’s also been a while since there was an update on the miui (MIUI Global 10.2) on my phone.

I’m not doing anything heavy at all so nothing should be justifying this kind of ridiculous drainage…

Any advice will be appreciated,
thank you!!