Bicycle Battery Case Castings

An e-bike battery case must shield the lithium battery cells from mechanical impact during riding on rough terrain, prevent moisture and mud ingress that could cause short circuits, dissipate heat generated during charging and discharging, and maintain its geometry under the compressive force of the battery retention mechanism. The aluminum casting contributes to all four: structural rigidity resists impact, the sealed parting line and mating surfaces control moisture pathways, aluminum's thermal conductivity assists heat dissipation, and dimensional stability ensures the case clamps correctly without warping.

The near-cubic form (66×56×53mm) with relatively uniform 2.8mm walls and no high-precision bearing or threading features means the as-cast blank can meet the ISO 8062-CT3 tolerance requirements directly from the die, without needing machining to correct distortion or achieve interface precision. Eliminating CNC also removes the risk of machining through the dense cast surface into more porous subsurface material—important for a housing where internal density affects both structural integrity and moisture resistance.

Unlike the thin, planar lever or housing parts in the bicycle series, this case has significant depth in all three directions (66×56×53mm), meaning the internal cavity is deep relative to the part footprint. This requires longer core pins to form internal features and careful venting design at the deepest points where gas tends to trap during fill. The roughly equal depth and width also means the parting line runs through the middle of all four sides—making parting line appearance management critical on a part where all exterior surfaces are consumer-visible.

The case mates with a cover or frame component, and the interface must be flat and consistent enough to compress a gasket or O-ring uniformly around the full perimeter—any flatness deviation or parting line step disrupts the seal and creates a moisture ingress point. The precision assembly requirement means critical mating surfaces must be free of excess material, flash, or coating buildup that would cause uneven seating. This is why both A-side and B-side appearance approval is required: the exterior surfaces that look clean also happen to be the mating surfaces that must seal correctly.

Lithium battery cells generate heat during both charging and high-load discharging, and elevated internal temperatures accelerate capacity degradation and increase thermal runaway risk. The aluminum case conducts heat from the cells to the outer surface where it dissipates to ambient air—functioning as a passive heat spreader. This is one reason aluminum is strongly preferred over plastic for e-bike battery housings: plastic is thermally insulating and traps heat, while aluminum's conductivity actively manages the thermal environment inside the battery pack, extending cell life and improving safety.