mac powerbook battery can die if the laptop is off?

Could it be that the machine didn't shutdown correctly so while you thought it was switched off it was still on therefore using some power and gradually draining the battery. Happens to my laptop sometimes but normally i notice and switch it off properly.

if your battery is old it will not give you an accurate time about how much time you can use it. you have to recharge it.. if it's lifetime is short you can change it with new one

Whether the laptop is a Windows based or Macintosh based system the battery is notoriously the most unreliable part of the construction. Many laptops end up with a battery that either fails to hold the charge or does not even charge. My own laptop battery is defunct, so I simply use it with a cable all the time. I realise that this is not the way a laptop should work, but sadly it is often the only option.

If the battery is kind of old and can't hold a full charge, it definitely could die if it's left for two hours after being run on battery. Plug the AC back in and check to see if the unit will come back on. If not, restart it and see how much (if any) charge is left in the battery, and if it will charge back up to 100%.

No I don't think that the battery can die if the laptop is shut off. I don't have a mac, but I have a laptop and if it's turned off the battery power remains the same as the last time .