Don't repeat other's expensive mistakes. I contacted some experts on car conversions and they were determined to sell me components that would make my car about 1400 pounds over weight. The batteries were 6 volt, lead acid, golf cart types which weighed 70 pounds each and I would need 18 for a total of 1260 lbs.
Each one has at least a 100 amp hour rating. Now, it takes 2 of these in series to match the 12 volt at 100 amp hour. In series the current remains the same and voltage sums. That would be 140 lbs of battery to provide (volts x amps = power) 1200 watt hour. Compare that to 1 Odessy battery rated at 68 amp hour, 12 volts. Again, volts x amps = 816 which is less power but, the weight is only 50 lbs. Now consider what is most important; the power to weight ratio as follows. Divide power by weight and look at the results. The units of measurement do not matter as long as, you do the same for both batteries. The expert's battery yields this number = 8.5714285
The smaller battery that I selected has this power to weight ratio = 16.32
So you see, the the bigger number means more power per pound of battery weight. My battery wins and I only need 9 batteries or 450 lbs. But wait there is more. Their motor was also heavy; 150 lbs which exceeds the original engine weight. It required 170 volts at 600 amps to produce 70 HP and 5500 rpm. The fact is, since the batteries can't supply that much voltage or amps, the effective horse power is a fraction of the peak rating and I only need 3700 rpm.
I selected a motor that weights only 39 lbs and produces as much as 19 HP at 72 volts. I only need 6 batteries so that is 300 lbs. I could carry ten people on top of the car and still not weigh more than the expert's car.
My batteries can supply this 39 lbs motor to operate at peak.
This is an experiment I will let you know how that works out. There might be heat issues.Next consider the number of batteries and the weight of each plus the battery boxes that hold them all plus the motor weight plus everything else you put in. 1400 lbs of extra weight will crush a normal suspension so you would need to add some heavy hydraulic struts and some more heavy steel to the strut towers. The adapter plate was solid heavy steel. Uhmm, I think aluninum and carbon fiber composite is lighter? The longer I talked with the experts the more I realized that they were thinking that the more weight the better. Could I just fill the car full of cement or lead? I wondered. No! So, think of the car as you would an airplane. The lighter the better because drag increases with weight and according to the laws of physics, the energy required to accelerate a mass increases exponentially as mass increases.
There are many different batteries and motors. You will have to use the specific numbers for each to see where you stand but, in the end the gross weight should be less than what you started with. Otherwise, the range of the car will be less than 60 miles to be certain and the cost to build the car will be more than the Leaf would cost you brand new off the car lot. The Leaf electric car has a range of 100 miles and it is loaded with air and power steering, navigation gizmo, etc. Call me crazy but, there is no point of doing any less for more money.
Either way, have fun!