Electric Credit Access Ready at Sale Act of 2021 or the Electric CARS Act of 2021 This bill modifies and extends tax credits for electric cars and alternative motor vehicles. The bill extends the tax credit for new qualified plug-in electric drive motor vehicles through 2031. In addition, the bill modifies the credit to remove the limitation on the number of vehicles per manufacturer that are eligible for the credit, allow a taxpayer to assign the credit to a financing entity, and allow an unused credit to be carried forward for five years. The bill also extends through 2031 the tax credits for (1) alternative fuel vehicle refueling property, and (2) alternative motor vehicles.