Groupe de cellules faible ou hors service dans le pack

One section of the traction battery has lost capacity, developed high internal resistance, or failed outright, while the rest of the pack remains serviceable.

A pack is a long series string, and a series string is only as good as its worst member. Every cell group carries the same current, so the weakest one reaches its lower limit first on discharge and its upper limit first on charge. The module has to protect it, which means the whole pack stops early in both directions — so one bad section out of many presents as a pack that has lost a large part of its usable range. The car is not exaggerating and the other sections are not faulty; the arithmetic of a series string simply works that way.

The characteristic signature is divergence under load rather than a low number at rest. A weak group often looks acceptable sitting still and drops away sharply the moment current is drawn, recovering when the load goes — which is high internal resistance rather than lost capacity, and the two are distinguishable if anyone bothers to look.

Whether this ends in a module or a whole pack depends on the vehicle, and it is the question to ask. Many designs allow a single failed module to be replaced and the pack rebalanced, at a fraction of the cost of a new one; some do not. Before accepting a complete pack quote, ask whether module-level replacement is supported — and confirm the sense wiring has been eliminated first, because a faulty measuring wire produces exactly the same reading.