Battery slowly draining on AC power then laptop (running Ubuntu) drastically slows down when it hits 30%

So all of a sudden my AC charger is not able to keep my battery charging when I'm using my laptop anymore. My Laptop is an Acer Aspire 5 A515-51G-72DB and I bought it brand new 5 years ago. It slowly drops down the battery level from 100% until it hits 30% then it stops dropping the battery level but instead the laptop becomes really slow and I have to suspend it and let it charge again. Some people told me that this issue is caused when your battery has completed all its cycles (or something like that) and then the OS detects it and sets the power settings to power saving. So I decided to rep

Question by Alexandre Lutosa on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.