One of the most common problems we see is that the notebook power cord is broken. This can be caused by the notebook being connected to the power cord while used on a soft surface, like a blanket or quilt on a bed. This can bend the cord upwards at sharp angle.
The problem is that too sharp an angle can eventually cause the wires within to break, which is usually quite obvious as the cord will then become quite floppy in that area.
To keep your power cord working well, try and avoid bending it unduly, and if you do roll it up, try and roll it up the same way each time.
Repeated bending in different directions will also weaken the metal wire inside the cable, eventually resulting in breakage.
Try and use your notebook on the battery at least 1/4 to 1/2 of the time. If you don't "exercise" the battery, then they quickly become less efficient, and the battery life will reduce.
My last notebook still had a 3+ hour battery life and the original power cord at 7 years old! This was just by taking some extra care with both the battery and the power cord. See if you can make yours last longer!