ORIGINAL: chaz5500
If you have a pack that's getting old and you are concerned about it, no big deal. just replace it, they aren't that expensive these days.
What would be considered old?
Tough to say really. I have a couple packs that are almost 4 years old and still hold very close to their rated capacity. One that recently failed is just under 3 years old. time is one factor but so is the number of cycles the battery has been through, whether it has been used in any extreme conditions, been through any trauma, etc. My basic point is that, if you have doubts, receiver packs for typical sport planes aren't very expensive to replace.