I did little research on it...and I read that the tracks of these races are alot shorter? Apparenetly because they batteries these cars run on will run out very quickly in a regular F1 size track.
Think about it this way, 1 kilogram is equal to 1 liter (of water but lets keep it simple). And a real F1 car can burn no more than 105kg per race, and they're typically coming in with about 5 gallons left due to fuel testing rules. And believe it or not F1 gas is pretty much the same stuff you're going to be putting in your car, just you know extremely tightly controlled and regulated to make sure no one gets any bright ideas for some extra performance.
So in the course of about the 90 minutes to two hours it takes an F1 car to win a race they're going to suck down about 100 liters of fuel. Thats about 26.4 gallons. In terms of energy density a gallon of gas has about 100 times the energy density, by weight and volume of a lithium ion battery, and 500x the density of a lead acid battery.
Your standard road car is going to have a thermal efficiency of about 15%, an F1 car on the other hand is the pinnacle of the internal combustion engine and is going to have a thermal efficiency of around 45%. Your average electric car is going to have an efficiency in the 90 to 95% range, but its fueled by power plants that have a thermal efficiency of about 30% ish.
So we have next year's formula E battery at 54 kWhr, which incidentally will allow Formula E to do away with the mid race car swap out. And drivers are allowed 200 kWhr used for the entirety of the race; the energy recovery technology on these cars is just this side of the magic/sufficiently advanced technology divide. We'll be generous and say that Formula E has 100% efficient power usage for their cars.
So gasoline has about 46.4MJ of energy per kilogram for a total effective expenditure of 2088 mega joules of energy at 100% efficiency from gasoline during a race. (Note I'm not including the KERS system into my calculations because I'm trying to keep this simple.)
And this is why SI units are amazing.
1 Megajoule = .28 kWhr
So 2088 Megajoules = 580 kWhr of energy.
Long story short a Formula E car has about 34.5% of the energy budget of an F1 car that is not running KERS.
The answer to your question is that yes Formula E races are shorter, they are also much slower than F1 races as well. Here's a handy graphic that helps explain.