RE: 6v receiver pack
A couple of things.
1. NiCd batteries have a graceful decline and can supply quick demands very well. They also have a "memory" so need to be cycled every 30 or so flights, maybe every month if you fly a lot. Charge slowly for longest life.
2. NiMh batteries have a definite "knee" in their discharge curve and will under great load decline rapidly that can lead to brown outs of the receiver. They do not develop memories and do not need to be cycled. Charge slowly for longest life. Need to go through several slow charge cycles and discharges to "form the battery."
3. EELOOPE NiMh do not like to supply a lot of power (peaks) at one time. Otherwise, they are just as good as normal NiMH.
So I would recommend (a) use NiCds of 2000 milliampere hours capacity five cell (6V batteries) for your normal four or five servo set up airplane.
(b) if you use NiMh the get 2500 milliampere five cell (6V) batteries for your normal four or five serve set airplanes. For Eeloope I would go up to a 2500 milliampere five cell (6V) battery and treat them like regular NiMh batteries.
I lost an airplane due to premature discharge of NiMh battery. My fault. Today I know better. 6 volt batteries are better than 4.8 volt batteries. The standard 4.8, 600 milliampere battery is marginal at best in an airplane with four servos. Yes, it will work and perform just fine for three maybe four flights, then it becomes marginal. Larger batteries capacity batteries are able to deliver more power for longer times thus become much more reliable. Capacity is measured in milliampere hours not the max or min voltage.
Good luck in Iran!