RE: FUTABA Telemetry
The Futaba radios that offer low voltage failsafe will typically just move the throttle to a low position. You can reset for about a minute by moving the stick to low and then back to high. The 12 and 14 channel radios allow you to set a battery failsafe (B-F/S) for all channels. Otherwise the other channels simply hold their last good position.
This feature operates at about 3.8 volts. The Futaba FASST receivers have been shown to continue to operate down below 3 volts. Some digital servos (non-Futaba) will stop working at 3 volts.
I have suggested several times to Futaba that they make this feature adjustable by the user so that you can set the voltage to a more useful one for your battery system. I mostly fly using 2S LiFePO4 packs and if I get to 3.8 volts my packs are essentially dead. I have never had this feature actually operate for real while flying, but it is there.