i've had my macbook for a little under a year and i think i may have shortened my battery power. i have a tendency to leave my laptop plugged in long past the fully charged time and allow it to run through the battery till it shuts down. i do this when i accidentally fall asleep listening to music or leave for work and forget it's on or plugged in. how hard on the battery or laptop is it to do this repeatedly? when it's fully charged it tells me i have roughly 4 hours of battery power available. is that the right amount? is there anything i should do to protect the battery? the manufacturer warranty will be up in march, should i take it in for a check up while i may have the option of not having to pay for it? any advice?