ORIGINAL: JohnBuckner
The best possible use for Questionable flight or Tx batterys is something like this simple servo driver/exerciser or even just a spare battery pack kept charged and convienent to the work bench for powering up an aircraft while working on it:
Never in a airplane you actually intend to fly.
Yup...
Questionable NiCD / NiMH packs can be disassembled and the individual cells ( once tested ) are great for glow ignitors, bench testing, and even for electric starters...
But for RX/servo electronics? No way.