Use energy consumed and your tariff. If the scooter uses an illustrative 0.035 kWh/km and you ride 8,000 km a year at an illustrative blended ₹9/kWh, annual energy cost is 8,000 × 0.035 × 9 = ₹2,520. Replace those example inputs with your scooter’s measured consumption and actual tariff.
For comparison with petrol, use the same annual kilometres and realistic fuel efficiency. The running-cost advantage can be large, but ownership value still depends on upfront price, finance, service access and resale.