RE: 4.8V versus 6V for receiver battery?
Usually, the radio system comes with a battery. The capacity of that battery is sufficient for general applications and maybe three flights before charging. Depends on how daring you are, I guess.
Higher capacity (mah ratings) provide more time. So, anything larger than what came with your radio is probably going to be just fine.
I use a Venim 1200 mah 5 cell (6 volt) NiMH battery pack. It weighs about the same as a smaller NiCd pack but lasts longer because of the capacity. I also use Voltwatch to keep an eye on the battery condition before and after each flight. It gives a quick indication of battery charge and lets you know if you are approaching the point where it requires charging.
CGr