Why can't I properly calibrate my smartphone battery?

Question

Rechargeable batteries

I bought a new battery for my phone (Honor 6c). the previous one swelled up.
The battery is 3k mAh, when I set it in the settings I looked at how much the phone would be discharged, there the phone could last 15-18 hours by 50+% (before calibration). I started charging up to 100%, several hours passed, and the phone was charged up to 99%, and then nothing, if you keep it on charge longer, then the maximum charge dropped to 98%, then I looked that the phone from these 98% could hold 18 (otherwise and less) hours, although on the last battery with a full charge, the phone could last 30 hours.
What have I done wrong?
I have always calibrated phones like this, now I calibrated 3-4 times, but now the phone is discharged from 96% in 12 hours
PS I calibrated like this: At the beginning, I charged to the maximum, then I tried to quickly discharge, launching heavy applications and videos, then I charged and discharged, and so 3-4 times