Some reciever pack questions

[speed demon]

I tossed my CC ubec because it was messing up and have decided to just stick with a small reciever pack. I have wired up 4 AA nimh in series which under load gives me 5.1v. I have one 40mm fan and one 30mm fan along with a futaba 2.4 reciever. The problem is my range stinks; well it's just not as far as my old stock AM radio. I think the problem is the reciever is suppose to run on 6v. So the questions are....should I just add another AA or try two small A123? http://www.radicalrc.com/shop/?shop=1&cat=199

I would like to use the A123 because it will cut down charge time plus be lighter but I think the volts might be too high. Can I just charge them to 3.1v and still have plenty of mah left? I really doubt I'm even drawing 1.5 amps with everything but I just don't know. Any help would be great. thanks.