The 3 parts are the adapter, battery and motherboard. The cost rises as you replace each part.
You didn't reveal the age of the machine and battery. Besides the number of charges, the batteries also have a finite shelf life. And some last longer than others. The consumers push for lowest prices means this part is also getting quality cuts.
For awhile now my battery has not been holding a charge. I must have my laptop plugged in to use it. I can have it charging for 24 hours but as soon as I unplug it the laptop is dead within 15 minutes. I thought laptop batteries lasted forever as long as you kept them charged? Am I wrong. Do I need a new battery, or could it be something else?