Plug-in electric vehicle (PEV) is emerging as one of the most viable choices for the transportation sector to reduce fossil fuel consumption and CO2 emission. As the most critical component of PEV, battery systems require intensive management and diagnostics to ensure safety, efficiency, and endurance. Most existing studies focus on battery management when PEVs are under operation while none has explored battery maintenance during overnight parking, which accounts for a majority of the time (> 12 hours per day). Battery states during this period significantly affect the lifetime due to the side reactions that occur even when the battery is not in use. The process occurs at an accelerated rate when the battery energy level or temperature is too high or too low. In this paper, we propose to utilize an existing infrastructure available to PEV owners, the home charging unit, for intelligent battery maintenance during overnight parking. We will design an optimal charging profile that would charge the battery to a specific level while maintaining its states at optimal conditions to minimize degradation due to side reactions over the whole overnight period. Optimal charging profiles are created for different ambient temperatures and at different stages of battery life to investigate various scenarios. To demonstrate the effectiveness of the designed optimal charging profiles, the total capacity loss overnight is compared with those of three standard charging profiles.