The performance degradation and durability of a Li-ion battery is a major concern when it is operated under radiation conditions, for instance, in deep space exploration, in high radiation field, or rescuing or sampling equipment in a post-nuclear accident scenario. This paper examines the radiation effects on the electrode and electrolyte materials separately and their effects on a battery's capacity loss and resistance increase. A60Co irradiator (34.3 krad/h) was used to provide 0.8, 4.1, and 9.8 Mrad dose to LiFePO4 electrodes and 0.8, 1.6, and 5.7 Mrad to 1 M LiPF6 in 1:1 wt% EC:DMC electrolytes. This study shows that the coin cells assembled with irradiated components have higher failure rate (ca. 70%) than that of control group (ca. 14%). A significant battery capacity fade post irradiation was observed. The electrolyte also shows a darkened color a few weeks or months after irradiation. The discovery of this latent effect may be significant because a battery may degrade significantly even showing no sign of degradation immediately after exposure. We investigated electrolyte composition by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and nuclear magnetic resonance spectroscopy prior and post irradiation. Polymerization reactions and HF formation are considered as the cause of the discoloration.