Laptop Battery, Charger or Faulty Plug?

My parents have a Gateway NV52, every time you plug in a charger it makes this “beep” indicating you have a power source plug in or when you unplug the power source. Though, last month the “beep” sounds is doing it constantly when the charger is plugged in and it ONLY happened when I turn it on or out of sleep mode. It beeps or like a good 5 minutes (like a car waiting to heat up). I unplug the power source and it doesn’t make the beep though my battery is slowing degenerating giving me only a amount of 17 minutes. Also, taking the battery out still cause the problem. This laptop doesn’t go anywhere so I rather not buy both battery and charger unless its a power plug issue that is faulty or has a loose wire.
Answer #1
Get a digital multimeter (A decent one would cost you $10 or less) and use it to test the charger as explained here:
https://learn.adafruit.com/multimeters/voltage
Set it to the 20 DCV (DC Volts) range. If you can’t get the probe to fit into the inner part of the jack (Which can happen with some of em) then just use a metal paperclip and bend it accordingly (DO NOT insert it while it’s plugged into the wall socket however!) after it’s in, Just plug it to the wall and do your testing (Have the correct probe touching the paperlcip and the other on the outer, base of the jack.) Also, Make sure you don’t actually touch the metal part of the probes or the paperclip while you’re doing it (It’s not gonna kill you, But you’d get zapped by it, So better not!)
Anyways, Good luck.
Answer #2
20V or less will not even zap him. Only bad thing from short-circuiting inner and outer part of the plug will be some small spark and overloading the charge, which might blow the fuse somewhere inside it. And those things are ~ censored ~ to open.