Modules vs. cells

A traction battery is not one big battery. It is built from smaller pieces stacked together.

Cells

A cell is the smallest unit, a single sealed battery. One cell is only a few volts, so you need a lot of them to reach hundreds of volts.

Modules

Cells are grouped into modules. A module is a block of cells wired together in one housing, often with its own connections and sometimes its own sensors.

The pack

Modules are wired in series, end to end, so their voltages add up. In one EVTU case study, 9 modules of about 30 V each made a pack of about 270 V (EST).

Why this matters

Because packs are built from modules, they can often be serviced piece by piece: modules come out, get tested and charged one at a time, and a single bad cell can sometimes be replaced instead of the whole battery. EVTU services packs of this type.