If you are talking about a 5 cell NiCd or NiMh then yes you will be fine. In fact, JC rec. that you run a 5 cell (6 volt) pack.

I myself run two a123 cells for my rx and servos and have yet to have any issues. I think you will find there are several guys both jets and large scale airplanes that run the A123 cells.

You will need a special charger for them as they are LiFe cells.

If you are just going to run a 5 cell pack you will be fine. Just make sure the pack is up to the "job" at hand. (good shape)

hope this helps.