Understanding your energy density result
Why gravimetric and volumetric density tell different stories
Gravimetric density, measured in Wh/kg, matters most when weight is the constraint, like portable or rooftop installations. Volumetric density, measured in Wh/L, matters most when space is the constraint, like a tight utility closet or a vehicle, exactly the kind of dual constraint the van life battery sizing calculator works within for a build where both weight and space are tight at once. A pack can score well on one and average on the other depending on its internal layout.
Why cell-level and pack-level numbers diverge so much
The battery cells themselves reach the highest density figures you'll see advertised, but the finished product adds an enclosure, cooling, wiring, busbars, and a battery management system that all take up weight and space without adding capacity. That overhead typically knocks 30 to 40% off the cell-level number by the time you reach a finished pack, a packaging-overhead gap NREL's energy storage research has documented consistently across manufacturers, which is why the power density comparison tool draws the same cell-versus-pack distinction for power output.
Why NMC leads on density but not on every metric
NMC's cobalt-based chemistry gives it a real edge in energy density over LFP, typically 20 to 30% higher gravimetric density, which is why it still shows up in weight-sensitive applications like electric vehicles and portable equipment, a tradeoff covered further in the EV battery degradation vs home battery comparison. That same chemistry trades away some of the cycle life and thermal stability margin that LFP offers, covered in more depth in the LFP vs NMC cycle life comparison.
What to check next
Once you know your pack's density, the footprint size comparison shows how that translates into real installation space, and the weight comparison tool checks it against structural limits for rooftop or upper-floor installs. The materials science behind squeezing more density into a smaller, lighter pack is an area the DOE's Office of Electricity continues to fund as storage demand grows.