How long have you had it? If you actually use the battery on a regular basis it's normal to see battery health go down. It's also just an estimate as well as not "real time". I've personally seen the number go down about 3-4% at a time. Some reports are that it can go down in succession as it "catches up".
92% is pretty normal and there's generally not much you can do about it. At this point Apple doesn't authorize battery replacement (even when the customer pays) unless the battery is considered "depleted" (under 80%) or otherwise fails.