I would say if the pack is getting old, doesn't balance easily and takes longer to charge than it used to, get rid of it.
I had 2, LiFE packs fail this weekend only 2 minutes into the first flight of the day after being freshly charged. Other than
the packs being about 4 years old and recently starting to take longer than normal to finish charging they appeared to be fine.
I noticed the engine starting to cut out (it's powered by the receiver packs via an IBEC) and landed immediately.
Engine died while taxiing back and by the time I had brought the plane back to the pits I no longer had control of the plane. I checked
the voltage and both packs read 3.3V! I unplugged them from the receiver and recharged them and they both were back down to
less than 6 volts within an hour (no load). Just glad I was able to get the plane back on the ground without any damage. Since
my transmitter supports telemetry, you can bet all my planes with have a telemetry for receiver voltage installed before they fly again!