Windows – Sony Vaio: Battery Level stuck at 80%

I've contacted Sony Support staff, and with his indication - something wrong with the service, I look into the services that got disabled, and I did found one - Vaio Power Management Service, after making this service running automatically, things went back to normal. I still don't know how the hell it got disabled though. I didn't fiddle with it.

This is a sign of battery degradation. If you look at the cat output, design capacity of your battery is 2250 mAh while the last full capacity is 1759 mAh. That's approximately a 21.8% degradation of battery life.You should perform a battery calibration to ensure that you have current and accurate information about battery wear.

Basic Calibration Instructions

Calibrating — or recalibrating, really, as the battery was calibrated in the past when the battery had more capacity — involves letting the battery run from 100% capacity straight down to almost dead, then charging it back to full. The battery’s power meter will then see how long the battery lasts and get a much more accurate idea of how much capacity the battery has left.

Source: howtogeek.com