No 4 rechargeables are no good. Add a 5th and you're looking at a good homemade rx pac. Its pretty easy to do, take some short pieces of 18ga wire and solder the cells together with teh wire, pos to neg. Add the wires you'll need to take off the alkaline holder you've been using and it will make a good rx pack.

Some companies like Balistic Batteries offer a rx pac made from 2700mah AAs. You can always zip tie the pac to something if you don't have the room in the rx box.