my original battery from my >1 y.o. MBP was replaced in march because it kept shutting off when not charged on AC. The new battery has been fine until now. after 40 cycles the health is down to 50% and it only holds charge for 1.5 hours. this is compared to only a week ago when it had a health of >90% and held charge for 3 hrs. ive tried calibrating the battery and resetting the SMC but the battery health does rise. http://www.apple.com/batteries/notebooks.html says "A properly maintained Apple notebook battery is designed to retain up to 80% of its original capacity at 300 full charge and discharge cycles". is this normal? should it be replaced? my MBP has past the warranty but can my 8 month old battery still be replaceD?