Structural Battery Pack
A structural battery pack is a traction-battery pack engineered to carry part of the vehicle's structural loads. It participates in body or chassis load paths instead of serving only as a separately mounted energy container. SAE International: Structural behaviour of cylindrical-cell battery packs
Where the boundary lies
An underfloor position, a strong protective casing, or numerous body fasteners does not by itself make a pack structural. The defining point is an intentional contribution to vehicle stiffness or load transfer. The direction and degree of that contribution vary, and a structural pack can still contain modules. Structural describes the role of the Battery Pack in the vehicle, not the choice between module-based and cell-to-pack construction.
Structural battery pack is a generic engineering description. Cell-to-body (CTB) and cell-to-chassis (CTC) are architecture labels used by manufacturers and suppliers, with boundaries that are not applied consistently. BYD, for example, describes its CTB system as combining the Blade Battery with the body floor so the battery also acts as a structural component. BYD: SEAL Cell-to-Body battery integration
Structural integration can reduce duplicated floor or support structure and improve packaging, but it changes crash validation, sealing, repair procedures, and load-sharing requirements. The results depend on the implementation, not the acronym.
For the broader construction and configuration trade-offs, see Battery Pack & Configuration.