An offline authentication of batteries includes communicating an encrypted authentication request to secondary batteries and a vehicle controller by a primary battery of an electric vehicle. The encrypted authentication request is decrypted to obtain a first random number and a fleet flag. An encrypted authentication response, including a first random number, a second random number, and a vehicle identifier, is communicated to each battery. Each battery verifies the first random number and the vehicle identifier. An encrypted battery status, including the first and second random numbers and an authentication status, is communicated to the primary battery that verifies the first and second random number and the authentication status. The primary battery communicates an encrypted authentication message to the secondary batteries and the vehicle controller. The secondary batteries and the vehicle controller verify the first and second random numbers and the authentication status for authenticating each battery.