A structural battery that simultaneously carries mechanical loads while storing electrical energy offers the potential of significantly reduced total vehicle weight owing to the multifunctionality. Carbon fiber is employed as negative electrode of the battery and also as a composite reinforcement material. It is coated with a solid polymer electrolyte working as an ion conductor and separator whilst transferring mechanical loads. The coated fiber is surrounded by a conductive positive electrode material. This paper demonstrates a methodology for addressing mechanical stresses arising in a conceptualized micro battery cell during electrochemical cycling, caused by time dependent gradients in lithium ion concentration distribution in the carbon fiber.