All rechageables only put out 1.2 volts, compared to 1.5 on an alkaline. An alkaline will give you a 12 volt reading, but for a very short time. I know that the recargeables should only read 9.6v. But, on a fresh set my JR reads 11.0 volts. It will hold that for a long time. Since it was meant to run on 12 volts, if it drops below 10.0v it will beep at you.

Yes you can use rechargeables, in your RCs. But, I would suggest you look into a higher mah rating.

I bought 4 1800 mah AAs for my digital cam about 2 years ago. They worked great. I then thought about my RCs. I did some more searching and bought 16, 2200 mah AAs. 8 for the TX and 8 for my 2 RCs. This was before RX hump packs were common, so this leaves me with two sets for the JR TX I have. I can go a long time on one set. About three times as long as the RX pack.

The mah rating is what you want to look at. If you can get them over 2,000 they should work well in both the RX and TX.