[all variants] Electrical (?) problem on a Dell Latitude 5420

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http://ubuntuforums.org – Hi, I have a very annoying problem on my laptop Dell Latitude 5420. It works perfectly fine when the battery is 100% charged (and plugged) or when it is unplugged (thus the battery is discharging). However, when in charge (and lower than about 90%), the computer almost cannot be used: the mouse moves incredibly slow (similarly for the touchpad). Furthermore, it seems that the hard drive responds very slow: saving a tiny text document (which would usually take a few milliseconds) takes 10-20 seconds. When I'm at work, the computer is always plugged, and this is not a problem; however, after I (Hardware)