08 MBP shuts off at 30% battery

alright, my macbook pro was purchased in the summer of 08, and i would say i've taken pretty good care of it. I typically just use the computer on the charger, taking it off the charger and cycling the battery every couple days or so. However, over the last semester, I noticed a dramatic change in my battery's ability to hold a charge.

so here's my problem...

My laptop will shut off with no warning when the battery's charge gets around 30%, sometimes even 35 or 40%. I don't receive a low battery indicator or anything.

Info (directly after booting back up from battery failure):
Manufacturer: Sony
Device name: ASMB012
Full charge capacity (mAh): 2201
Health Information:
Cycle count: 241
Condition: Check Battery
Battery Installed: Yes
Amperage (mA): 1517
Voltage (mV): 12173

so what should i do about this? i don't think i should have to buy a new battery after a year and a half of normal use.

"condition: check battery"

people always ignore this -_-

go to apple, get a new battery for free. Its under warranty by sony. Be sure to have a genius appointment. I got my new battery the day i went in.

dang, 241 cycles!

thanks man, good to know i'm covered. as for the check battery indicator, i did... indeed it was still attached to my computer