Some LFP batteries now get rated for 5000 or more cycles or more. Even if you cycle them fully every day, that's 14 years. And that's unlikely to be needed or happening. These might last decades. At which point, battery tech might be massively better. Also, even better batteries might be on the way. E.g. Sodium Ion would be a bit less energy dense and have a similarly long life. It doesn't contain any lithium and could be cheap to manufacture in a few years. The biggest driver here would be cost and other properties (like how quickly can it deliver the power and at what capacity).

It's irrelevant how long they last unless is starts to substantially exceed human lifespans though. 10 years or 20, eventually every product you put out there is replaced and you enter the steadystate waste phase of X tons per year.

Personally of course, I don't think this matters at all: old lithium batteries degrade into salt and don't contain harmful chemicals. There's no real indication we'd ever have a problem dealing with them, even if it was just throwing them all into a big hole till the hole looks enough like a natural lithium source to mine again.

Lithium batteries last as long as one battery out of thousands decides to thermal runaway, and then you have to replace all of them (as well as the facility they were all housed in).