That really depends on the cell type. With OPzS they’re rated to 80% DoD, with C100 as the standard capacity rating used. You’re right that plenty of traction and gel cells get pretty tired pretty quickly with moderately deep cycles - I’ve just educated a friend on exactly this, as he killed two 12v batteries inside of six months by undersizing his storage and drawing too deep - 70% DoD daily on AGM batteries is murder.
In our application, we rarely go below 20% DoD - but we could take them much, much deeper without unexpected implications for their life.
The other nice thing about OPzS is they they’re each a single 2V cell. Means you can monitor for and track down individual duff cells, rather than having a whole battery fail. After 9 months, ours are still perfectly balanced, gravities all identical when charged to when they were new, literally zero problems.
Interesting that you can get a decent number of cycles with 80% DoD. I've seen estimates that put a big drop just going from 45% to 55%, so I assumed going further would just be cell suicide. TIL!
Monitoring is also a nice benefit. I wonder if at some point it would make sense to put bypass diodes on cells (like solar panels have) so that dead cells won't bring down a pack.
