It is apparently a very common problem when your laptop can't be fully charged. When I had to fix my laptop ac adapter I searched all over the internet for a solution. I found quite a few forum threads and laptop reviews discussing the issue but no one actually fixed it themselves. Lazy bastards. Most of these folks were having them sent in for warranty work and having the entire main boards replaced. This is a ridiculous waste of money for someone.
I did see an ad for some computer repair place who was charging $200 to fix these, which is a total rip off. They were replacing the jack (claiming $20 just for the part!!) which is not necessary (at least not with this one). Well, I am really cheap and I didn't want to deal with the time or BS of having it shipped (the warranty is expired anyway), so I fixed it. Cliff's notes at bottom.
The power led on the front would flicker when the laptop AC adapter was plugged in. I could wiggle the power cord and it would change the nature of the flickering. Sometimes it would stay on continuously and sometimes it would shut off depending on the wiggling. This behavior had the obvious side effects of shutting the computer off and never really charging the battery. Oh how irritating.
At first I thought it was the laptop ac adapter power cord. I mean I could wiggle the cord and it made changes to the flickering, so why not? After testing it with the volt meter it seemed to be good, good enough to not spend ~$85 on a new power cord. The laptop ac adapter jack in the machine turned out to be the culprit. Well, sort of.
Technically it was the connection between the jack and the main board. Yeah, just a stupid connection. Not the whole motherboard like the corporate "customer service" reps want you to think. See, the laptop ac adapter jack has the positive connection coming out of the back and directly into the board with a little weak solder joint keeping the jack from rocking back and forth.
When the laptop is subjected to normal amounts of laptop ac adapter power cord wiggling it breaks the weak joint and screws up power delivery. You can test this by plugging in the laptop and pushing the end of the cord in different directions while watching the green power light.