Tank vs battery efficiency

Useful motion per unit of stored energy

Headlines use the same definitions as the bars: petrol = chemical energy in the tank; EV = DC energy drawn from the high-voltage pack (charging losses are on the cost-per-km page).

Petrol (tank-to-wheels)

—%

of chemical energy in the tank

EV (battery-to-wheels)

—%

of DC energy from the pack

Useful-energy ratio (EV / petrol)

—×

same trip assumptions via shared “urban” sliders

Where the energy goes (100% stacked)

Petrol: combustion heat and exhaust · transmission and final drive · friction brakes (no recovery). EV: cell internal resistance and auxiliaries · inverter and motor · optional friction brake use; regen reduces net energy drawn from the pack (caption under the EV headline).

Petrol — heat / exhaust / pumping

Petrol — gearbox and driveline

Petrol — brakes (no regen)

EV — pack + aux on discharge

EV — inverter and motor

EV — friction brakes (remainder)

Useful at wheels (both)

Petrol path

Chemical energy in the tank to torque at the wheels. Modern spark-ignition engines typically deliver on the order of a quarter to a third of fuel energy to the crankshaft in mixed driving; the rest is mostly heat.

Tank to crankshaft (chemical → usable torque) 32% Broader literature band ~25–38% for SI engines in real cycles; slider is your one-knob stand-in. Crank to wheels (transmission, differential, tyres) 92% Urban / stop-go mix 35% How much of the trip behaves like repeated accel/brake. 0% = steady motorway cruise. Braking energy (share of trip budget lost as heat at brakes) 12% Scaled by urban mix. ICE cannot recover this; you burn fuel again after every stop.

EV path

DC energy from the traction battery to mechanical power. Motor + inverter figures are often quoted ~90–97% peak; the pack always wastes a few percent on I²R and power electronics.

Pack discharge loss (cells + BMS + auxiliaries) 4% Inverter + motor (battery DC → mechanical) 93% Regen capture (fraction of recoverable brake energy) 55% Not motor efficiency — how much decel energy gets back to the pack in this driving mix. Highway driving leaves it near 0. EV friction brake use (share of braking handled by pads) 8% Stronger regen and one-pedal driving drive this down; emergency stops still use friction.

Methodology and limits

Boundary. This page stops at the fuel tank and the traction battery. Refining, petrol delivery, grid generation, and wall-to-battery charging losses are out of scope here; they sit in operating cost and lifecycle GHG models.
Petrol heat. The “tank to crankshaft” slider folds together indicated thermal efficiency and mechanical friction losses before the gearbox — a teaching simplification, not a single map point from an engine dyno. See e.g. Heywood, Internal Combustion Engine Fundamentals for typical thermal splits; on-road BSFC maps differ by load.
Regen. Recovery depends on speed, pack state, blend strategy, and how often you use friction brakes. The headline EV % divides useful work by net DC from the pack: gross draw (inverse of the bar’s useful fraction) minus a return term tied to recoverable losses. The stacked bar stays a gross path so regen is not drawn as a negative slice.
Not a range predictor. Real-world L/100 km and kWh/100 km on Plug or Pump already embed driving style. This page holds the fuel tank or pack fixed and shows how much of that stored energy reaches the wheels before dollars or grid CO₂e enter the picture.

Model in efficiency.js; physics numbers are computed in your browser.