Depth of Discharge (DoD)

The inverse of state of charge

If a pack is run from full down to 20% remaining, that is an 80% depth of discharge. Run to 60% remaining, and it is a 40% DoD. DoD and state of charge are two views of the same number.

The reason it gets its own term is that DoD is the variable that governs degradation, and it is the one a fleet operator can actually control.

Shallow cycles buy disproportionate life

Lithium degradation is not linear in energy throughput. Two half-depth cycles are considerably gentler than one full-depth cycle, even though they move the same total energy.

The practical consequence is counter-intuitive: a rider who tops up opportunistically will get more total lifetime energy out of a pack than one who runs it flat and charges overnight, despite the first rider performing far more charge events. Cycle counts are a poor proxy for wear precisely because they ignore depth.

This is also why published cycle life figures must state the DoD they were measured at. An 800-cycle claim at 100% DoD and an 800-cycle claim at 60% DoD describe very different cells.

What to do with it

Specifying a pack: oversizing capacity is a durability strategy, not just a range strategy. A pack sized so typical use reaches only 60% DoD will outlast a smaller one worked to 90%, often by enough to change the replacement economics.

Operating a fleet: mid-shift charging is a longevity measure. Where the duty cycle allows it, opportunistic topping up beats deep daily cycling — see our notes on delivery fleet duty cycles.

Storage: neither extreme is kind. Long-term storage at full charge or near-empty both degrade cells; a partial charge is the right resting state, and it is worth writing into your warehouse instructions rather than assuming.