I noticed the past few days my Netbook isn't giving me any battery warnings when its getting low. I used to get it saying 12% remaining, 10% remaining, 8% remaining 5% critical plug in before blah blah blah. Now it jut shuts off on me without any warning and goes to hibernation.

Did you remember tweaking the low battery warning notification under power management?

I haven't touched anything in regards to any battery settings.

on my netbook, a led become red when it's remaining 15%, but isn't give any signal.

Which netbook did you use? I believe Caperjack has the right solution for you.

I don't know exactly what happened but in the end i just reverted it back to the default settings then changed the settings back to the way i wanted them and the battery warnings starting appearing again.