Notebook Hardware and Upgrade Questions

Hello!

I have a problem with the battery, but let me tell you the story from the beginning.

In the past I was using my laptop daily, but these days I rarely use it.

I never shutdown my laptop, so sometime I set the laptop on sleep mode and go, and after few days I try to turn it on, but it doesn't because the battery is empty, and sometimes I set it on hibernate mode, and the same thing occurs , but with hibernate the battery lasts longer.

Well, in these days this thing occurs usually, almost everytime I try to turn it on, this thing occurs.

And now I'm facing a problem I thing it's connected to that thing ("I try to turn it on, but it doesn't because the battery is empty").

The problem is when I charge the laptop, battery percentage never goes beyond 81%, it reachs 81% and stop there, even after half an hour the percentage doesn't change.

It's not a bad for me if the problem only is that the battery percentage never goes beyond 81%, but I'm worried that the problem is bigger, I mean the problem may be bigger in the future, and what happen when the laptop is plugged, but the battery doesn't increase, what happen for the electericty that flows if its really not charging the battery, it's must be going somewhere.

I thaught that maybe the problem is with the namber that showen near the battery icon, so I generated battery report using cmd with the command powercfg /batteryreport and its says that the battery is 81%, 33,510 mWh

and 33,510 is 81.46 from 41,149 (this number is the full charge capacity, this information is also from battery report).

I want to know if someone knows this problem, or know how to solve it, or what it's cause. 

EDITED:

I discovered something new about the problem, It doesn't "never goes beyond 81%",  the real problem is "from 81% the charging speed become very slow, if the battery is 81% after one hour it become 82%, and also if the battery is 81% or higher, if I use my laptop during charging the battery will stuck at 80% because the charging speed from 81% and higher is slower than the consumption speed.