# Electric and hybrid vehicles: Science and limits

Why a battery car wastes so little, and hydrogen so much

Source page: https://www.materialinsights.org/energy/e_evs/science/

What this tab covers What physically happens in the conversion, step by step, the science behind it, and the hard limits that physics sets on how well it can ever work.

A battery car delivers about two thirds of the electricity it draws from the socket to the wheels, close to nine tenths counting reused braking energy, against 18-25% of fuel energy for a petrol car. A fuel-cell car loses far more, because electricity becomes hydrogen and back.

#### The conversion, step by step
**Charging**
Electrical (grid AC) → Chemical (battery) · about 90% on the US combined test; ADAC (2026): over 93% at a wallbox, as low as about 75% from a household socket^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml)^[12](https://ecomento.de/2026/08/07/adac-untersucht-elektroauto-ladeverluste/)**Inverter, motor and gearing**
Chemical (battery) → Mechanical (wheels) · losses equal to 18-22% of socket energy (combined cycle); accessories take a further 3%^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml)**Regenerative braking**
Kinetic → Chemical (battery) · net 22% of socket energy reused (combined), 32% in the city^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml)**End to end, battery car**
Electrical (socket) → Kinetic · 65-69% direct, 87-91% counting regeneration^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml)^[2](https://www.energy.gov/cmei/vehicles/articles/fotw-1360-sept-16-2024-typical-ev-87-91-efficient-compared-30-conventional)**End to end, fuel-cell car**
Electrical (renewable) → Hydrogen, electrical, kinetic · 25-35%, against 70-80% for a battery car (Volkswagen estimate)^[11](https://volkswagen-newsroom.com/en/stories/hydrogen-or-battery-5545)

#### The science

Charging pushes lithium ions into the graphite anode, storing chemical energy; driving lets them flow back while electrons flow through the motor circuit. An inverter turns the battery's direct current into three-phase alternating current whose rotating magnetic field turns the motor. Losses are mainly resistance heating (rising with current squared), transistor switching and magnetic losses in steel. Run backwards, the motor is a generator, so braking recharges the battery. A full hybrid adds a motor and small battery to a petrol engine so the engine runs near its best point, stops instead of idling and recovers braking energy. A fuel cell turns hydrogen and oxygen into electricity on a platinum catalyst, but making hydrogen loses about 45% of the electricity and the car loses about 55% of the rest.

#### Limits set by science

| Limit | Value | Why it exists | Best today |
|---|---|---|---|
| **Road load (physics of moving a car)** | about 14 kWh per 100 km at the wheels at a steady 108 km/h (calculated)^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml) | Drag power = 0.5 x air density x drag area x speed cubed; rolling power = rolling coefficient x weight x speed. Assuming 1.2 kg/m3, 0.6 m2, 1,800 kg and 0.01 at 30 m/s: 9.7 kW drag plus 5.3 kW rolling, 15 kW in all (calculated). | At 65-69% socket to wheels, about 21 kWh per 100 km from the socket at this speed (calculated) |
| **Fuel cell ceiling** | 83% (calculated: Gibbs energy 237.1 kJ/mol over enthalpy 285.8 kJ/mol, higher heating value)^[11](https://volkswagen-newsroom.com/en/stories/hydrogen-or-battery-5545) | Part of the reaction energy must leave as heat; catalyst and membrane losses add more. | About 45% of hydrogen energy reaches the drive (calculated from 55% lost, Volkswagen estimate) |
| **Regenerative braking** | at most the car's kinetic energy, less motor, inverter and battery losses in both directions^[1](https://www.fueleconomy.gov/feg/atv-ev.shtml) | Drag and tyre losses during the stop are gone, and friction brakes take hard stops. | Net 22% of socket energy recovered on the combined cycle, 32% in city driving |
| **Charging losses** | under 7% at a wallbox; 13-15% for most cars, almost 25% for the worst, from a 2.3 kW household socket^[12](https://ecomento.de/2026/08/07/adac-untersucht-elektroauto-ladeverluste/) | Fixed loads (charger electronics, battery management, cooling) weigh more when charging slowly. | Renault 5 lowest in ADAC's 2026 test; Mercedes CLA worst at a household socket |

#### Sources

1. [Where the Energy Goes: Electric Cars](https://www.fueleconomy.gov/feg/atv-ev.shtml) US DOE and US EPA (fueleconomy.gov), 2025
2. [FOTW #1360: A typical EV is 87%-91% efficient compared to 30% for a conventional gasoline vehicle](https://www.energy.gov/cmei/vehicles/articles/fotw-1360-sept-16-2024-typical-ev-87-91-efficient-compared-30-conventional) US Department of Energy, Vehicle Technologies Office, 2024
3. [Hydrogen or battery? A clear case, until further notice (company analysis)](https://volkswagen-newsroom.com/en/stories/hydrogen-or-battery-5545) Volkswagen AG, 2019
4. [ADAC untersucht Elektroauto-Ladeverluste (report of ADAC's 2026 AC charging-loss test of five cars)](https://ecomento.de/2026/08/07/adac-untersucht-elektroauto-ladeverluste/) ecomento, 2026

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_evs/index.md)
- [Overview](https://www.materialinsights.org/energy/e_evs/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_evs/correlation/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_evs/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_evs/economics/index.md)
- [Engineering methods](https://www.materialinsights.org/energy/e_evs/methods/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_evs/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_evs/links/index.md)