I've had my Mac for a little less than a year now, it is a Macbook Pro 17in, it is like the one with 1gb of RAM, rather than 2 gbs. Whenever I would use it when it was not plugged in I would dim the screen significantly and it would estimate my battery life around 4 hours. But very recently I do the same thing is it is always estimated at less than 2 hours, and after about 10 -20 minutes or less of use it shuts off. I try to turn it back on and it makes the initial noise, then dies again. It also seems like it takes a long time to charge up back to full, but I don't have any issues with it when plugged in...any ideas?