If it will fit in the case it won't be a problem. 9.6 volts is 9.6 volts, A 2500 mah pack can produce more amperage than a 600mah pack but that's not an issue as the transmitter will only draw a specific amount and no more(unless there is a problem like an electrical short inside). So a 2500 mah pack will run longer between charges than the 600.