Would you buy a new battery for a very old laptop?
I just got a pretty good deal on an old ThinkPad (think 10 years old now) to use as a beater for screwing with ArchLinux and hopefully to find a real use for. It's in great shape like it was never really used, but big shock, the battery is at 50% effective capacity and what's there disappears in less than an hour.
Would you bother buying a battery replacement for it? On one hand I want it to actually be usable on the go because that was sort of the point. On the other, while replacement batteries exist, I'm worried that they're already very old themselves and already "expired". Would you take the chance? I don't want to let this thing go to waste when it's still perfectly usable, in fact it's pretty fast.
Absolutely do not start ripping apart your old laptop battery to replace cells if you don't know what you're doing. Depending on the battery size and type, you might also not have many cells at all to replace.
You would be better off buying a cheap replacement battery, especially if it's already 10 years old. Any cells that aren't bad today will likely be very soon.
Telling people to pop open a Li-Ion battery is asking for a fire.
What does that have to do with anything? You gave dangerous advice to someone with unknown skill levels for handling batteries.
But yes, I do, and if you don't know what you're doing and puncture a cell trying to take the wrap off, you'll have a bad time. Li-Ion fires are terrifying, and it makes no sense to replace a few cells when you can just get the whole damn battery for a few dollars more and mitigate the risk of burning down your house.