Pushed by federal regulations, automakers are spending billions to develop new all-electric cars. But with gas prices staying relatively low, consumers aren’t buying the electric offerings available now. Except for the glamorous and expensive Tesla Model S, electric vehicle sales for the first half of 2016 are down 11 percent, according to Kelley Blue Book. (Tesla doesn’t report monthly sales, but estimated Model S sales are about even with last year.) However, the major drawbacks…