I think all the accessories mentioned here can reduce your fuel mileage somewhat. The whole idea is to find a balance of using the accessories you payed for and purchased but with some idea that fuel economy will decrease with their use. Having heated seats, for example............sure beats using them and loosing some efficiency when compared to freezing until the ICE heats to normal operating temperature! AC and most of the other accessories will not have as much a drain on the battery(s). The lights will drain some......obviously, but again they are not something you can turn off at night!!