basically, my battery is 100% charged per the menu bar on the top right. but, when i unplug the ac adapter, the powerbook shuts off immediately. i have a new 3rd party battery. it worked perfectly fine and then...baaam!!...now this. i called apple care and they said that i might need a new battery. i don't believe what they are saying since this is brand new and it used to work like a charm until as of recent. any help?