Random FPS drops on Acer Aspire E5-571 when plugged in

Hi,

So I've had this problem since I got this computer and haven't been able to solve it. Basically, when I am playing a game and my computer is plugged in, then my fps will randomly drop from around 60 to around 10. If I run off of battery power then I stay at 60 fps. This even occurs when the battery is disconnected and I am running only off the AC adaptor. I only experience these issues when playing games like Counter Strike or Dota 2 and not, for example, Undertale (which is much less intensive). It also does not occur when watching videos or browsing the internet.

I have tried changing the power plan settings, changing the maximum power management settings and upgrading the graphics drivers. I am running windows 10, but this problem still occurred before I updated from 8.1. Could it be an issue with my charger? One reason I think it might be is that it never displays the correct time untill fully charged (right now it says 01 minute untill fully charged, despite the fact I only have a 65% charge). I have also considered trying to update the BIOS (the current version/date is Insyde Corp. V1.09, 7/11/2014).

Any help would be greatly appreciated.