I was asked to participate in design and approval of an electric conversion for a 172. Though it seems to have gone quiet, I learned quite a few peripheral things while I studied the concept. A big one was charging batteries. The problem is that either you have to swap heavy and expensive batteries to keep the plane in service, or it's down for hours charging after a half hour flight. Training aircraft don't generate revenue while they're parked charging. Swapping several hundred pound batteries will involve heavy lifting, and probably a dented airframe at some point. Putting the batteries in place of fuel tanks in a Cessna would be difficult to impossible. It's a logical place, but hardly an easy do. A whole bunch of screws for a 152/152/172 fuel tank cover, but not possible for a 180 and on.
The authorities were very eager to support the concept with regulatory flexibility. For example, at present, an "engine" must be type certified to be eligible for a certified aircraft. I can't certify a motor to the engine design standard, so I can't use a type certified powerplant in the installation. Previously a project stop, but the authority really wants to give on this point, among others.
It'll happen, and I look forward to it, but it's a ways off for commercial application just yet.