At pickup, a customer whose slightly puffy battery was converted to a replacement asks why the shop made such a fuss — the old pack still held a charge and the case still closed over it. What is the section's actual answer?

Select one answer.

• Liability policy — shops cannot legally return a device containing any battery that has changed shape, regardless of its condition.
• Capacity honesty — a swollen pack has lost most of its usable capacity, and returning it would have meant returning a phone that dies by noon, which is a warranty callback wearing a battery's name and the quiet commercial reason every professional bench converts at the first visible sign of a dome regardless of how well the pack still happens to measure on the bench that afternoon.
• The dome is decomposition gas pressing on a stressed separator — the micrometers-thin film that alone prevents the cell shorting through itself — and mechanical pressure on it is the failure's own trigger. A breached cell heats itself and supplies its own oxygen, so the fuss is the only window where the fix is still a routine swap instead of a containment event.
• Charging behavior — swollen packs overcharge because the gas insulates the thermistor, and the fault would have cooked the replacement port.