Laptop randomly shuts down

[MAdummy]

I've been having issues the past few months where my laptop will randomly shut down when i don't have it plugged in. I originally thought it was my battery and bought a new one and it still does it with the new battery. It will randomly shutdown with 80% battery left and even when i power it back up it'll stay on for awhile then power off again. I took off the bottom plate to see if it was overheating or fan was clogged, fan was clean and bottom wasnt hot at all. So i'm kinda stumped.

My laptop is (originally had windows 8 64-bit):
Asus N551JQ-EH71
Intel Core i7 4710HQ (2.50 GHz) - 16 GB Memory - 750 GB HDD - NVIDIA GeForce 845M 2 GB GDDR3 - windows 7 64 bit

all help is very much appreciated and a big THANK YOU in advance!

 

[Grobe]

Assuming this is a "sudden shutdown" - opposed to a controlled shutdown orchestrated by windows.

Little over a year ago, I bought a cheap used Acer aspire that inhibited the same issue. After trying about any possible things I could think of, I was never able to figure out what was wrong. In the end I just scrapped the thing as it was unusable.

Later on, I figured it may have being some "thermal rubber things" that pushes CPU/GPU and chipset IC against the motherboard when assembled that was getting permanent deformed due to old age.
I never got the time to actually test this theory, and other rubber parts not original may not stand the heat.
Nb: your laptop may be constructed otherwise.