I have a JR 4.8v 1100mah Nicad pack, 4.8v 2500mah Nimh pack and a 4.8v 2000mah. I have only used the JR RX pack of 1100mah and have been able to get a full days flying (5 or so flights) no problems. I think if I had a 600mah pack I would be getting worried. So my answer is to get a big capacity RX battery pack and you can insure if you charge the batteries with a peak detection charger the night before you will have no problems.