I am pretty sure the answer will be "It doesn't matter, voltage is voltage" but want to make sure I am not missing something. Can I use a 6.6V LiFe Rx pack in a Tx? I know the Tx packs have some sort of overload protection that would prevent them from working well as Rx packs, but I am going the other way. Both the Rx and Tx packs are 6.6v 2S LiFe packs so I would think there would not be any issues.

That's what I use in my 4pls no issues

Sure, but Rx packs are usually a lot lower capacity than a Tx pack, so don't expect a lot of run time.

Cool, thanks. It is a 2100 so it should be fine for a little while as little as I get to run nowadays.