Mild hybrid technology is now commonplace on petrol and diesel engines, providing improved economy and performance. Mild hybrids have very small battery packs compared to full hybrids and EVs, and at no point is the car driven solely on electric power, so the performance of the car is affected very little by the condition of the battery. We would expect it to last for many years without replacement, so although a replacement would be more expensive than a conventional 12V battery, unless you plan to keep the car for 10 years or more we would not expect this to be an issue.