Li-ion energy storage: 4 hour limit

I read a fair amount (OK, actually a lot) of stuff about renewable energy and related topics. One thing that I frequently encounter is that grid-scale Li-ion batteries have a limit of 4 hours of use. Or charge or something along those lines. But I’ve never really understood exactly what that means. Is this a physical limit? I don’t think Li-ion batteries will self-discharge in only 4 hours if the power isn’t used first. Fairly certain they won’t. Is it some kind of economic limit?

It sounds like a combination of economic and chemistry. This link hints of some fo the reasons

Which include that Li-ion batteries will have a shorter lifespan at times over 4 hours discharged (pg 9). That sort of makes sense as what kills Li-ion is heat and spending time at low states of change (and also near 100%). It’s the total time the battery spends at those conditions, not just being there, but how long. While in grid use I would suspect that the batteries can get hot, and if the batteries have more capacity they would be hot for longer time and that could shorten life.

The other part also hinted at earlier on is that these batteries are chosen because they basically do well for short duration power requirements, they fit that bill nicely, but just because that doesn’t mean they are well suited for other applications. 4 hours seem like the limit where the economy starts really dropping off, most applications are designed for less then 4 hours ideally.