Energy Density
Definition
Energy storage capacity per unit mass (Wh/kg, gravimetric) or per unit volume (Wh/L, volumetric). Key performance metric for mobile applications.
Why It Matters
- Primary metric for weight-constrained applications (UAVs, aerospace)
- Achieved at pack level is 60-80% of cell-level due to packaging
- Tradeoff with power density, safety, and cost
- Improves with advances in cell chemistry and packaging efficiency
Common Pitfalls
- Quoting cell-level energy density when pack-level matters
- Not accounting for BMS, cooling, and structural mass
- Sacrificing safety for energy density
- Not considering degradation of energy density over life