**George Baure and Matthieu Dubarry \***

Hawai'i Natural Energy Institute, SOEST, University of Hawai'i at Manoa, 1680 East-West Road, POST 109, ¯ Honolulu, HI 96822, USA; gbaure@hawaii.edu

**\*** Correspondence: matthieu@hawaii.edu; Tel.: +1-808-9562349

Received: 31 March 2020; Accepted: 13 May 2020; Published: 15 May 2020

**Abstract:** The usage of electric vehicle batteries to assist the main electric grid for the storage of energy provided by intermittent sources should become an essential tool to increase the penetration of green energies. However, this service induces additional usage on the cells and, therefore, could degrade them further. Since degradation is path-dependent, it is of paramount importance to test the impact of all the different grid applications on the batteries. In this work, we tested the additional usage induced by using electric vehicle batteries for frequency regulation at moderate rates during rest or charge and found no detrimental effect after around 2000 cycles on the cells.

**Keywords:** lithium-ion; dQ/dV; dV/dQ; frequency regulation; V2G; G2V; electric vehicle
