RE: Mattel Pulse Radio
The receiver is set up for 3 volts. If you use more, or less voltage, it will affect it's performance. More voltage will make it distort the recived signal and subject to noise overloading it. Less voltage will cause a drop off of range, and actuator power.
There are two bias resistors which can be changed in value to allow operation at 2.4 volts, 3.0 volts, and 3.6 volts. Ace receivers had this as a factory option you could have done. I myself would use an LM317 voltage regulator set to 3 volts and a Lipo. It's either that, or use two AA sized Alakaline Energizers, as most planes need the weight up front anyway.