I had previously been hire to work on certification of an electric conversion for a 172. We got a long way down the path, but the ultimate problem was going to be down time for charging. There are commercial realities of using an airplane for 45 minutes, and then having it off line for several hours to charge. For a private airplane, where the owner wants to fly 45 minutes a day, it would have been perfect - but that's a lesser market right now.
The electric conversion project I'm currently involved in recognizes this operational reality, and is planning to account for it - for now - while they wait improving battery technology. It'll come, and some very forward thinking aviation entrepreneurs are working to create a market. There are other certification [regulatory] adjustments to be made, though I find that the regulators are very receptive.