This sure sounds like CYA, or marketing. I've had some equipment long enough to actually wear out the packs and it's usually more than 5 years, but less than 10 before they give up. Not sure what the specific issue is after 5 years but if it holds a charge and runs the gear, then I have no need to replace it. I've had some lithium packs swell, maybe this is the issue they're heading off but I don't need a calendar for that, just my eyes.
Mark K5LXP
Albuquerque, NM