A look at the key elements of a battery pack enclosure design. This design will change based on the size and application, but it is still worth approaching this from a high level.
One of the first things is to look at all of the parts required for a battery. The major systems are:
- Cells
- Module (physical part or virtual group of cells in case of C2P)
- Battery Management System (BMS)
- Cooling system
- HV cables/busbars
- LV cables
- HV control system
- Pack enclosure itself
- Mounts
- Labels for inside and outside of the case
The high level functions can be grouped into:
- Mechanical
- Electrical
- Thermal
- Chemical
- Safety
Mechanical
The enclosure has to carry the static weight of the cells, cooling plate and busbars, plus the dynamic and vibration loads of the vehicle in service, without the base plate or side walls deflecting enough to load the cells themselves. Where the pack sits low in the vehicle it also has to survive underbody impact – a kerb strike, a piece of road debris, or a scrape over an obstacle – without the intrusion reaching the cells, and in a crash it needs to resist deformation that could crush or short a module. In cell-to-pack and cell-to-body architectures the enclosure additionally becomes part of the vehicle’s structural load path, so its stiffness and mounting points are a body-in-white design input, not just a battery one.
Electrical
The enclosure has to maintain safe creepage and clearance distances and electrical isolation between the high-voltage system and the (grounded) case, which is normally verified against an isolation resistance target set out in standards such as ISO 6469-3. HV connectors and any exposed conductive parts need finger-proof (IP2X or better) protection, cable entries need proper strain relief and shielding, and the case itself needs a defined, low-impedance path to the vehicle chassis ground for both safety and EMC reasons.
Thermal
Day to day, the enclosure needs to support the cooling system interface (typically a cold plate bonded to the base) and insulate the pack from ambient temperature swings without trapping heat generated by the cells, busbars or BMS electronics. Where a thermal interface material is used between cells and the cooling plate, the enclosure’s dimensional tolerances directly affect how consistent that thermal path is from cell to cell. In an abuse event the enclosure also has a thermal role in slowing propagation between cells – see Physics of Thermal Runaway.
Chemical
Materials used in and around the enclosure need to be compatible with everything they might contact over the vehicle’s life: coolant (usually a glycol-water mix), road salt and washing chemicals on the outside, and electrolyte or decomposition products on the inside if a cell ever vents. See Pack Enclosure Materials and Plastics for how specific material choices hold up against these exposures.
Safety
Beyond keeping water and dust out – typically to an IP67 or higher rating, see IP Ratings – the enclosure needs a defined, controlled path for gas and pressure release if a cell vents, so that a fault does not build up pressure and rupture the case unpredictably. Regulatory crash and post-crash safety requirements such as UN Regulation 100 also apply at pack level. It’s worth noting that a passing IP rating on its own does not guarantee real-world sealing performance over the vehicle’s life – see Why IP67 and AIS-156 Are NOT Enough.
See also: Pack Frame Giga Casting, Inputs to Pack Sizing