Rechargables run 1.2V per cell, so you will need 10,
Akalines run 1.5V percell so you only need 8
Lipo's run in config of 3.7V per cell, so 3S (3 in series) is 11.1V, 4S would be 14.8V and you would need a regulator of some sort.
New type LiFe's run 3.3V so a 4S pack would be 13.2, probably spot on for what you want.
Disclaimer, I have no experience with batteries on a XR600, just an RC junkie.