Read the exact battery warranty for the model: years, kilometres, any capacity threshold, exclusions, transferability and claim process. If your planned ownership ends inside a strong transferable warranty, automatically inserting a full battery replacement can overstate expected cost. If you plan to own well beyond warranty, model a downside reserve or lower resale value rather than pretending battery risk is zero.
Separate routine degradation from a rare major failure. Ask for battery-health information when buying used, and price uncertainty instead of inserting an arbitrary replacement every five years.