A strong hybrid can drive on electric power alone using a large battery and traction motor, while a mild hybrid cannot — its small motor-generator only assists the petrol engine during acceleration and restarts. The difference shows in fuel economy: strong hybrids save 35–45% fuel in city driving, mild hybrids typically under 10%.
How each system works
A strong hybrid (also called a full hybrid) pairs the engine with a sizeable battery — around 1–2 kWh — and an electric motor powerful enough to move the car by itself at city speeds through an e-CVT. The engine switches off frequently, and braking energy recharges the battery, so no plug is ever needed.
A mild hybrid replaces the alternator with a belt-driven integrated starter generator (ISG) and a small lithium-ion battery, usually 48V or less. It smooths the auto start-stop, harvests a little braking energy, and gives a light torque boost — but the wheels are always driven by the petrol engine.
Why it matters when buying
Carmakers market both as "hybrid", so check the spec sheet: if there is no EV-only drive mode, it is a mild hybrid. Strong hybrids cost ₹1.5–2.5 lakh more than equivalent petrols but routinely return over 20 km/l in city traffic, making them compelling for high-mileage urban buyers. Mild hybrids add little cost and little saving — treat them as an efficiency tweak, not a reason to pay a premium.
Indian examples
Strong hybrids: Maruti Grand Vitara and Invicto, Toyota Urban Cruiser Hyryder, Innova Hycross and Camry, and Honda City e:HEV. Mild hybrids: Maruti's Smart Hybrid variants of the Brezza, Grand Vitara, Ertiga and XL6, and Toyota's Neo Drive versions of the Hyryder and Taisor.