You are looking in the wrong place. The gases that batteries give off when charging are relatively harmless. The problem lies in where the electricity comes from to charge them. The answer? From power plants many miles away that are polluting many more times than a gasoline engine to do the same amount of work.
I have said this before, and I will say it again. Electric cars are only of limited value due to several factors. Short range, long charging times, limited amount of recharging that can be done to a given battery. Current battery technology is simply not up to the job.