RE: 6v or 4.8v reciever battery?
My 2 cents... love the hobbico field charger... I bought packs from cheapbatterypacks.com. I ordered 5cell (6v) hybrid NiMH 2100 mAh packs @ $15 ea. Work great, low self discharge and high capacity. I probably could fly every weekend for a month without charging them (although that would be silly). I top em off at the start of the day and not worry about them. I got a pack for my Airtronics rds8000 as well, stays at full voltage the entire day. Supposedly the hybrid NiMHs don't like high loads and can have voltage drop outs (maybe a capacitor can overcome this?). How much and at what current I don't know. For my 40 size no worries, but for a large scale high current warbird you may want to get some actual figures on that.
Have fun with your bird!