This paper proposes a blockchain-based method for assessment and tracking of electric vehicle battery degradation costs. Vehicle-to-Grid (V2G) technology allows the bidirectional flow of electric power between the electric vehicle (EV) and the electric grid. However, for making optimal charging/discharging decisions, it is essential to precisely evaluate the battery degradation. In the proposed method, the initial degradation cost is estimated based on the present status of the EV battery in terms of range and age. Following this, a degradation cost of the battery is obtained from battery specifications and continuously tracking the variables that affect battery energy capacity, which will determine the economic loss to EV users for participating in V2G programs. A Mixed Integer Linear Program to minimize cost includes this degradation cost in its objective function to make the optimal decision for an EV's interaction with the grid. At the end of each 24-hour cycle, the battery degradation cost is updated based on the charging/discharging transactions performed during the cycle and the temperature conditions. These transactions and battery degradation costs are stored in a consortium blockchain that is shared among the relevant actors.