I was on a team that built a lead acid hybrid race car in college. I seem to recall the batteries were by far the heaviest component of the car; at ~40lb a piec

I was on a team that built a lead acid hybrid race car in college. I seem to recall the batteries were by far the heaviest component of the car; at ~40lb a piece, they were more than half the gross vehicle weight (pilot and ethanol included). Assuming Pb-C is roughly comparable to Pb-Acid in mass density (since most of the weight is presumably in the Pb), then you'd need ~twice as much to match it in energy density. I'm wondering how massive the battery packs will end up being on such a vehicle. >The reason lithium is used for electric cars is energy density. This is not a problem for hybrids. I don't understand what leads you to conclude this.