When a smart badge project comes in, one of the first questions is often: “The battery bay is only a few millimetres thick. Can it still meet our capacity target?” Thickness alone cannot answer that. We also need the usable length and width, the space taken by the seals and tabs, and the current the badge draws when it reads a card, connects over Bluetooth or wakes its display. Start with the enclosure and the load, then work out the capacity.
Start with the usable battery bay
A Li-Po pouch cell contains layered or wound electrodes sealed in an aluminium-plastic laminate. Without a rigid metal can, its outline can be designed around a flat or narrow enclosure. That does not mean a finished cell can be cut to any shape: active electrode area, edge seals, tabs and insulation all need room. The device drawing is what tells us whether the proposed outline is workable.
For a thin badge, the useful feature is the freedom to match the cell footprint to the available space. The actual capacity still depends on the bay’s usable dimensions, assembly clearances and electrical requirements.
Thickness alone does not tell you capacity
Capacity depends on cell length, width and thickness, as well as electrode design and materials. Two cells with the same thickness can have very different capacities if their footprints differ. The housing also needs clearance for the seal, tabs, insulation and assembly, so the internal bay dimensions matter more than the outside badge dimensions.
For an initial review, send the usable length, width and thickness, a housing or CAD drawing, the tab direction and the space reserved for insulation and assembly. The proposed capacity should be tied to that specific outline and its test data; a general “capacity by thickness” chart cannot replace a cell specification.
As a cell gets thinner, the seals and internal layers take up a larger share of its total thickness, leaving less design margin. Alignment, finished thickness and sealing therefore need to be checked on the actual construction. Capacity, resistance and yield should come from the relevant sample and specification, not from thickness alone.