HP laptop slows down while charging

Laptop: HP EliteBook 8540w

O.S: Windows 10


After a year of buying this laptop, when the battery used to be lower than 80% Either plugged in or not, the system used to slow down to the point of being unusablegames and videos lagging, webpages become unresponsive and etc.. After a while, I started getting a warning message about the battery not working properly on startup so I replaced it with a new one. Laptop worked fine for few months then started having the same problem, only this time the system slows down only when the battery is less than 80% and plugged inworks fine when not plugged in. I only plug it in when it goes down below 10 or 20%. Slows down a few moments after plugging in.. What seems to be at fault here now? Because the problem now is a little different than before. Also the fact that laptop slowing down this much when the battery is low at all is something I never faced with previous laptops I owned. Is it the battery, AC adapter or the system itself?

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