A mild hybrid has a small battery and starter-generator that only help the engine; it cannot drive on electricity alone, so savings are small (Maruti's Smart Hybrid). A strong hybrid has a larger battery and motor that can move the car on electricity alone at low speeds and charges itself from the engine and braking, so city mileage improves a lot (Hyryder, Grand Vitara strong hybrid, Hycross). A plug-in hybrid has a bigger battery still, charged from a socket, for a useful electric-only range before the engine starts. axler8 counts only strong and plug-in hybrids as Hybrid.