Yeah turns out an electric drive train is much lighter than a gasoline one which offsets the battery weight somewhat. Gasoline engines aren't light, nor are the transmissions. Currently I think the weigh penalty is about 15-20%.

My guesstimate is if they can increase the energy density of batteries by 30-50% the weight penalty will disappear. Some of the reduction is the weight reduction of the battery and some is due to cascading effects on the rest of the car.