So presumably a 100uV drop in battery voltage would produce a similar frequency deviation. Assuming an approximately linear deviation of frequency with supply voltage then a 10mV drop (likely after only a short time of battery use, or even as temperature changes) would shift the frequency ~ 20MHz !!! Hardly a desirable feature (and of dubious legality)!Power supply ripple of only 100uVpp will produce about 200kHz of frequency deviation