If both packs failed after the first charge, I would suspect a problem with the charger or the charger settings. As the old saying goes, once is a coincidence, twice is a conspiracy!

I have no experience with and therefore can't comment on the LiFe's...

However, I would never plug a 2S Li-anything directly into a receiver. They are nominally rated at 7.4 volts, but with a fresh charge they are close to 8.4 volts, which over time -- if not immediately -- will damage your receiver. Imagine the amp draw if you are using 6 or 7 digital servos and then do a maneuver, such as a flat spin, where all of them are engaged fully at the same time!![X(]

-- Bob