The reason for the warning is that the servo can produce high-current draw from your batteries. Older NiMH cells had high internal resistance and with several servos, most notably digitals, the servos would draw enough current to drop the system voltage to below the receiver needed.

You should be fine with your choice of battery.


Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
[email protected]