Like any specification there is a tolerance band on battery capacity specifications. One of the unique things about batteries is the tolerance band is often sta

Like any specification there is a tolerance band on battery capacity specifications. One of the unique things about batteries is the tolerance band is often stated as being asymmetrical, since no one would reject a battery for having too high of a capacity (unless it's physically too large or something). So instead of a spec like "200 mAh +/- 10mAh" and the implied symmetrical distribution of real measured values, you get something like "200 mAh +20mAh -10mAh".