Many of the 25 year old servos will not take 5 cell receiver packs, especially JR. As far as brown out with 4 cell packs the only brand that has this problem is Spectrum. I fly Futaba, Hitec, and Airtronics on 2.4 and I have never had a brown out with a 4 cell pack. I belong to the 2nd largest rc club in the USA and I have never heard a non Spectrum user complain about brown out.