Nobody understands the point of hybrid cars

TL;DR

Hybrid cars achieve efficiency primarily through Atkinson-cycle engines, not batteries — the electric motors exist only to make that compromised engine drivable.

Key Points

• 1.The real secret to hybrid fuel economy is the Atkinson-cycle engine, not the battery. A modified Atkinson-cycle engine achieves 40–41% thermal efficiency vs. ~25% for a standard Otto-cycle engine, by keeping intake valves open during compression to allow greater expansion of combustion gases.
• 2.The Otto cycle wastes energy by limiting how far combustion gases can expand. James Atkinson's 1887 solution used exotic linkages to extend the power stroke; modern hybrids replicate this simply by tweaking intake valve timing.
• 3.The electric motors exist solely to compensate for the Atkinson engine's poor power delivery. The 2.5L four-cylinder in the Sienna produces only 186 hp in a way most drivers would find unacceptably sluggish — the motors add ~60 hp boost to reach 245 hp total.
• 4.Hybrid batteries are not a 'bank account' of stored energy — they're a small buffer. The Sienna's battery stays near 45% charge; the car avoids using it unless the driver floors it or the engine strays far outside its efficiency band, because conversion losses make unnecessary battery use wasteful.
• 5.Charging the battery from the engine is actively avoided because energy conversion is lossy. Every conversion step (mechanical→electrical→chemical→electrical→mechanical) wastes energy, so the car charges the battery almost exclusively via regenerative braking, which is 'free' energy.
• 6.Toyota's Hybrid Synergy Drive is mechanically simpler than a manual gearbox. It replaces the transmission with just two electric motor-generators (MG1, MG2) and a planetary gearset acting as a power-split device — no clutch packs, no belts, no gear changes.
• 7.The planetary gearset makes Toyota's system a parallel hybrid, not a series hybrid, which matters enormously for efficiency. The engine can mechanically push the wheels directly; a series hybrid (like the Gen1 Chevy Volt) forces all power through generator→battery→motor conversions, yielding only 35 mpg city/40 highway on premium fuel.
• 8.The Chevy Volt is a cautionary tale of series hybrid inefficiency. Despite being much smaller than the Sienna, the Volt's four-step energy conversion cycle gave it virtually identical fuel economy to the minivan — worse in dollar terms due to premium fuel requirements.
• 9.Toyota's all-wheel drive implementation has almost no efficiency penalty. A third 40 hp electric motor on the rear axle adds AWD capability; the EPA rating difference between FWD and AWD Sienna versions is only 1 mpg.
• 10.Plug-in hybrids only make financial sense if you can charge daily with cheap electricity. When running on gasoline, PHEVs have worse fuel economy than standard hybrids due to the weight penalty of their larger battery pack, making them a poor choice for those without reliable home or workplace charging.