I believe the above broad statement is flawed. Spektrum state that a 4.8 volt nicad must not be used, risk of drop outs, but the receiver CAN handle up to 10 volts. Voltage fed to the Rx is also fed directly to the servos on the 9100. So if using a 5 cell nicad/Nimh pack (upto 7 V fresh off charge) pack you may be OK, your choice, without a regulator BUT if using a two cell lipo, then you have 8.42 volts to the Rx AND servos and that voltage is too high for the servos so you need to regulate. (The Power Box manual expands on that) and MacGregor have issued a specific warning about the use of two cell Lipos, unregulated to the servos. You risk premature failure. Duralites also give 8.4V, too high for the servos without a regulator. The best compromise if regulators are not to be used seems to be A123s, high enough for the Rx to avoid drop outs and perhaps no too high for the servos to use unregulated !

Regards, David.