An automobile is a highly engineered collection of complex components, each of which has its own lifespan and longevity characteristics. The MTBF (mean time between failures) of some components is expected to be smaller than the life of the car, as the replacement of these is considered part of regular maintenance. Other components, which typically experience less wear, are expected to have a longer life; however, a large longevity may very well require replacement of several of these, raising issues of economics. The most expensive part of an electric car built in the 2020s is the battery, and its lifetime is expected to be about 16 years, or about 2 million kilometres (1.2 million miles) if the car driven a lot.