Apostolaki-Iosifidou et al. [1], published in the May edition of Energy, is an important contribution to the field of vehicle-to-grid (V2G). It is the first publication to document the roundtrip efficiency of V2G, a critical element for assessing its economic viability. Roundtrip efficiency was found to range between 53% and 62%. This contrasts with existing V2G economic analyses, which either assume roundtrip efficiency to be substantially higher, or ignore losses altogether. We highlight an additional source of energy loss not captured in the experimental design of Ref. [1]: unfavorable temperatures. Given the wide divergence between empirical findings and the assumptions employed in existing V2G economic analyses, we propose that existing analyses greatly underestimate the costs of implementing V2G and should be considered incomplete until re-specified with updated efficiency values. We show that even using the highest efficiencies found by Ref. [1], electricity losses offset more than half of the revenue from V2G frequency regulation in PJM, the most frequently studied ancillary service market for V2G operation. Researchers should employ findings in Ref. [1] for more accurately-specified V2G economic models. (C) 2017 Elsevier Ltd. All rights reserved.