By Mi-Young Park, CEO & Co-Founder, Sasung Power
85 to 100 kg is the approximate mass of enclosure and support hardware added to a standard floor battery pack for a 100 kWh passenger EV. None of that mass stores energy. It provides structural containment. Structural battery integration seeks to remove this overhead by placing cells directly in the load-bearing frame. The saving is real, but production results depend on the engineering constraints around that integration.
What the 85 to 100 kg Covers
A conventional floor pack's mass falls into roughly five groups: cell modules at 50 to 55% of total pack mass, the steel or aluminum enclosure and baseplate at 15 to 18%, thermal hardware such as cooling plates and fluid lines at 8 to 10%, BMS electronics and wiring harness at 6 to 8%, and mechanical mounting hardware at 4 to 6%. The cells remain. The other groups can potentially be removed when the pack becomes part of the vehicle structure.
In a flat-floor EV, a 100 kWh pack generally weighs 580 to 650 kg. In theory, load-bearing structural cells can remove 100 to 130 kg by replacing the standalone enclosure, separate cooling plate structure with through-structure channels, and mounting brackets. Structural integration alone therefore represents a 16 to 20% mass reduction, without any chemistry improvement.
What Structural Integration Removes
Once the enclosure goes, each related subsystem must be redesigned or removed. Cooling changes from a separate fluid loop and cooling plate to conduction paths through the composite structure. The BMS harness becomes shorter because integrated current collectors connect cell terminations directly to the vehicle electrical bus. Mounting hardware is no longer separate because the pack itself forms the structure.
Structural integration also introduces less visible mass. Carbon fiber composite adds approximately 10 to 15 kg per cubic meter of integrated structure compared with a steel enclosure, although it performs structural work at the same time and replaces frame material that would otherwise be required. The calculation is not simply "remove the enclosure and save its weight." It must also include the extra thickness needed for equivalent electrochemical performance in constrained cell geometry, electrical isolation layers between adjacent load paths, and added sensing infrastructure for cells under mechanical load.
Three Load Cases That Decide Net Savings
The saving holds only when integrated structural cells withstand real vehicle loads without extra reinforcement. Three load cases most often add mass in structural EV integration:
Torsional stiffness: A passenger EV floor needs roughly 15,000 to 22,000 Nm per degree for acceptable body dynamics. Carbon fiber composite cells with fiber layup aimed at electrochemical efficiency, whether random or biaxial, typically provide 60 to 70% of the torsional stiffness per unit thickness of a properly engineered structural floor. The choices are to accept lower stiffness, add a separate structural laminate, or change fiber orientation toward structural performance at some electrochemical cost. Each choice alters the mass budget.
Crash management: Side and frontal impact regulations set minimum crush zones and energy absorption targets. A pure cell structure absorbs energy through electrochemical degradation, meaning cell crushing, rather than controlled deformation zones. Hybrid designs place structural cells in a thin metallic crash rail. They weigh less than fully separate systems, but their crush behavior must be validated and is difficult to certify through simulation alone.
Fatigue loading: Road inputs apply cyclic loads across an EV floor that a conventional pack handles at its mounting points. A structural cell receives those loads across its full area. Carbon fiber composite performs well in tension over fatigue cycles but is sensitive to interlaminar shear during repeated bending. That is also the direction in which electrochemical cycling stresses the material through lithiation expansion.
BMS Sensing Costs to Include
Removing the enclosure creates another monitoring requirement. Each cell group in the load path needs voltage and temperature sensing plus awareness of its mechanical state. Under compression, a cell can show a 3 to 8 mV voltage offset from its unloaded value at the same state of charge. Without load-aware voltage correction, BMS state of charge estimation error grows in proportion to load variability.
With conventional 96s2p cell groups, a pack might use 192 voltage sense lines. Keeping the same cell count while distributing groups across frame sections adds at least 24 to 32 strain proxy channels to separate mechanical voltage offset from true electrochemical state. This adds wiring mass, though less than the enclosure mass removed. Early platform integrations measured the addition at 2.1 to 3.4 kg for a 100 kWh structural floor.
When Structural Integration Falls Short
Structural battery integration is a poor fit when cells must be replaced at module level on a short service interval, when asymmetric load paths concentrate stress in a few cells instead of distributing it, or when operating temperatures fall below -20°C without active heating. Carbon fiber composite also performs poorly thermally in extreme cold because the laminate has low through-thickness conductivity.
The point is not that structural integration outperforms conventional packs in every category. In a high-cycle urban delivery vehicle that replaces its pack every three years, structural cells' lack of replaceability can be a liability. The relevant question is whether mass saved per kilometer over the vehicle's service life exceeds the lost end-of-life replaceability. The answer depends on vehicle class, duty cycle, and maintenance model.
Why Mass Calculations Need Honesty
The 85 to 100 kg conventional enclosure overhead is real, and structural integration can recover most of it. The figure in the vehicle specification will be lower after accounting for reinforcement to meet torsional and crash targets, added sensing, and thermal redesign. Current platform designs can achieve a 12 to 15% net mass reduction through structural integration. The 20% headline requires a clean-sheet vehicle that co-optimizes frame and cell geometry from the start, not a retrofit of existing architecture.
This does not mean chemistry is irrelevant to battery performance. It means chemistry is not the source of this mass saving. The structure changes, requiring concurrent redesign of the vehicle frame, thermal system, and BMS sensing architecture. Each is a tractable problem on its own. The engineering challenge is running all three redesigns in parallel.