A battery powered C172 may well work for 1hr training flights in the battery endurance sense.
I just ran a few numbers.
Assume a C172 that's normally running on a 160 HP engine, at 70%. One HP = ~750 W. So in one hour, this aircraft uses 160 * 70% * 750 = 84 kWh. (Maybe a little less because of increased efficiency. But that doesn't change the discussion significantly.)
This energy needs to be replenished somehow. A typical European circuit can deliver 240V at 16A, which is 3.8 kW. This means that recharging that aircraft using a normal circuit will take a little over 22 hours.
So in essence, with that setup, the flight school can squeeze a single flight out of that airframe on any given day. Assuming they max out the 240V circuit for the rest of the day to recharge the aircraft.
Of course that's not a setup that's practical. But you need the equivalent of 22 average household circuits, all maxed out, to get a more-or-less workable charge rate of about one hour for each flight hour - assuming your batteries can charge that fast.
10 aircraft charging simultaneously and you're looking at values approaching one Megawatt. That's the unit that we normally express powerplant capacities in. (Fukushima Unit 1 was 460 MW, to give you an idea.)
As others have said, before electric flight really takes off, there are a few things that need to happen:
- Battery storage capacity needs to improve significantly
- The power grid needs to be upgraded significantly
And even then I think automotive technology is going to reap the rewards first, and aviation last.