Industry

Injection Molding for Battery Systems

A battery pack is rows of identical cells held in place by plastic. Every small error in a cell holder repeats across the whole row, and the plastic has to keep doing its job if a cell ever overheats.

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Level by level

From one cell to a finished pack

Each level adds a molded part with its own job.

1
Cell holder
A grid that spaces and locates cylindrical or prismatic cells. Spacing sets how heat moves between them, and every pocket has to match the next one.
2
Module frame
Holds a group of cells together under the pressure of cells that swell a little as they age. Stiffness and creep resistance matter more than looks.
3
Busbar carrier
Positions the metal links between cells and keeps them apart. It is often molded around the metal or snapped over it.
4
Pack lid and enclosure
Keeps water and dirt out, holds a seal, and on many packs carries a vent that opens under pressure.
5
BMS housing
Protects the board that watches every cell. It needs locating features for the board and clean routes for sensing wires.

Cell holders

Questions a cell holder drawing has to answer

Most first article surprises on battery parts come from one of these.

Is the cell held by a press fit, a snap, or adhesive, and which tolerance on the cell drives it
How flat the holder must stay across its full length after molding
Which flame behavior the pack design expects from the resin
Where cooling plates, pads, or adhesive touch the holder
Whether upper and lower holders are separate parts that must line up

Long parts

Why a long holder is harder than it looks

The problem is repetition, not complexity.

A holder for a long row of cells is a simple shape repeated many times. The plastic shrinks as it cools, and a small amount per pocket adds up to a large amount at the far end. If the pockets are sized at nominal, the last few cells do not fit.

The usual answers are a gate layout that fills the length evenly, a resin with glass or mineral filler to cut and even out that shrink, and a steel adjustment after first samples are measured. Planning for that adjustment is normal on these parts, not a sign something went wrong.

Holding the cells

Molded holders or potting the cells in place

Both are common. They lead to very different packs.

Molded cell holder

Cells can be located, inspected, and in some designs replaced
Repeatable spacing set by steel
Adds a tooling step and a part number

Potting compound

Fills gaps and damps vibration without a tool
Adds weight and makes the pack hard to rework
Cure time and mixing become process steps of their own

FAQ

Questions from battery teams

Which resins are common for cell holders?

Flame rated PC and PC/ABS for many consumer and storage packs, and glass filled nylon or PBT where stiffness and heat matter more. The pack design usually sets the flame requirement first.

Can the vent be molded into the lid?

The vent housing and seat can be. The membrane or burst element is usually a bought part fitted afterward, so the molded seat has to hold it at the right pressure.