If the battery is over 95% charged and you whack in the charger! The system still won't charge. Your battery has to be drained so it's under 95% before a charge is active.
the mbp batteries are weird anyway. don't let the 98% bother you. sometimes you can't do anything to fix the numbers. i have a 3 week old battery and it went from 100% health to 95-96% as soon as i calibrated it and that's where it stays now. oh well!
It's also possible that the error is not in the battery, but rather in the software you're using to monitor it. iStat gives me different readings at different times. 98% is close enough. Don't fret over it.