Physics nerd reporting in here 😛.
mAh = milli-amp-hour. A measure of the current the battery will be able to provide at it's operating voltage for one hour. ie, a 6800 mAh battery will provide 6.8 A of current at its particular voltage for a time of one hour.
What you really should be concerned about is the capacity of the battery in WATT-hours, this measures the capacity irrespective of voltage. What could easily happen is that the newer computers have batteries that supply current at a higher voltage (and because P=(V^2)I, a battery of the same capacity but a lower current will require a higher voltage to compensate). The newer models of Macbook Pros use a different battery layout with flat rather than cylindrical cells, and I wouldn't be surprised if there are more cells than the older batteries. More cells = higher supplied voltage. Though that is just me hypothesising, Apple don't exactly make that sort of info public.
Best thing to do is just leave your computer idle with display on 50% brightness, doing nothing but browsing light (ie no flash) websites. If you get the 8-9 hours or whatever that Apple claim, your battery is fine.
