I don't know what the benefit would really be, though. As I understand it, the only function of that number is when estimating the remaining battery life - and that seems to be kind-of a guess anyway, and probably will depend on the exact characteristics of the replacement-battery.
Also, it seems you _can_ set the figure to "3000" (though I doubt the batteries with "3000" printed on them are truly 3000mAh - given that all the 'extra large' batteries are roughly the same volume they are probably all about the same capacity, maybe 1900mAh?) by editing the 'fixed.cfg' file to put that in there.
I have these lines in my fixed.cfg file
battery capacity : 2000
max files in dir: 9000
Not sure if that truly does anything, mind.