The main thing is that in a warm climate, they drop off in capacity badly at about 2 years old. This can even happen if they were stored warm, and never used much.
But as long as they are not puffing, or full of dings and dents, they can still be usable up to 4 years old. It's just that they suck by then. They tend to have about half capacity by then, and can only handle a very very low c rate, like .5c. Any faster draw on them, they don't even put out half capacity. Also, they will take about 4v of charge, and after that they seem to just sit there on the charger for an eternity, not getting any more into them. They can still get more or less fully charged, but it will take forever. I'm not too sure you get the benefit of it, charging them full either.
So if you need is something were too heavy, and needing to use a ton of it at a time is the goal, it could be worth it if you have a big supply super cheap, ideally, free. But to carry old shitty stuff on the bike is no fun. Do that only if you have no other choice, and are desperate to add just a few more wh to your pack.
I run incredibly old and sucky lipo on my mower. With enough ah, it still works fine for that. I just charge them till I see the rate of charge slow a lot, and then pull them off to mow. Screw waiting for a full charge. This season, mowing with some 5 year old packs.
