i got a penryn mbp whose battery i should have replaced when the program was running but didnt. like coppola's "Jack" its aging way too quickly. in about 2 yrs it's down to 5% battery capacity in only 80 or so cycles. as i use it as a desktop replacement, i run it almost exclusively run it off the adapter, which probably helped to screw the battery. is it ok to have a nearly dying battery in the mbp? if the current capacity runs down to 0 will my machine be unusable until i get a new battery?