They could, though it would be hard to quantify. They all draw current from the HV battery, and that requires recharging. Recharging comes either from regeneration (which obviously won't be affected) or the ICE.
I've noticed that after upgrading my stereo I've driven the car more often than needed, which probably has had some effects on my mileage...
Like Jimbok said, it is hard to quantify. Sometimes I'm not sure if my milage loss is due to the weight of the stereo equipment or if it is from energy drain and at other times the milage doesn't seem to change at all which could be due to simple weather conditions or lack of careful driving. With my larger and heavier box in the car and playing it at high volumes it does seem to affect my milage but I have no evidence to validate my observations. To comprimise I simply run my large amp at 1/2 the ohm load I normally do for full power and I only run 1 speaker instead of two. Sound quality is still great if a bit lower in subbass volume. Since the vehicle is much more enjoyable to drive with a better stereo I say go for it.
If you figure your average power draw for the stereo, it will be easy to calculate the mileage hit. Tom
Because music is so dynamic, figuring out the average draw is tougher than it sounds. I was looking at a new Arc Audio amplifier that draws over 400amps peak. It puts out 4366 watts continuous so I guess the draw is understandable. I'm gonna take a wild guess and say that most average systems (under 600w rms) will draw less than 50amps continuously and judging by most systems I've seen in this forum will likely draw around 30amps continuous with short spikes in the 50-60amp range. This is my opinion based on the average size fuse we use to supply power to amplifiers and the fact they rarely pop.
