The Feature Everyone Switches Off Is Now on 63% of New Cars

You know the button. It's usually near the gear selector, often marked with an A wrapped in an arrow, and a large share of drivers press it before they leave the driveway — every single time, because it never remembers.

Automatic start-stop shuts the engine down when you halt and restarts it when you lift off the brake. Here's how fast it took over.

Four percent to sixty-three in twelve years, for a feature with no fan club.

It exists because of how the test works

Fuel economy figures come from a standardised laboratory cycle, and that cycle contains a lot of idling — it's modelled on city traffic. An engine that switches off during those pauses posts a measurably better number.

The gain is real but modest in normal driving: somewhere around 3–5% in heavy traffic, close to nothing on a motorway. On the test cycle it's worth enough to matter, and when you're a manufacturer trying to hit a fleet average, a few percent across every model is not something you leave on the table.

So it spread not because customers asked for it, but because the arithmetic of compliance made it nearly free to add.

What it does to the car underneath

This is the part that matters when you're buying used, and it rarely comes up.

The battery is different. A start-stop car needs an AGM or EFB battery built for hundreds of restarts a day. They cost roughly twice a conventional battery, and fitting a cheap standard one — which will physically fit — leads to early failure and erratic electrical behaviour. Plenty of used cars have exactly that fitted by a previous owner economising.

The starter works harder. Manufacturers fit reinforced starters and heavier-duty bearings for the duty cycle. When they do fail on an older car it's a bigger job than a conventional starter, because they're often less accessible.

Some systems age badly. On higher-mileage cars start-stop often stops engaging at all — usually because the battery has degraded past the threshold where the system trusts it. Owners frequently read that as the feature breaking. It's the car protecting itself, and it's a signal the battery is due.

What to check on a used car

If the system doesn't engage on the test drive, ask when the battery was last replaced and what type went in. "A battery" is not the answer you want — you want AGM or EFB, and ideally a receipt.

Then decide whether you care. If you do most of your miles on a motorway, the feature is doing nothing for you and switching it off costs you nothing measurable. If you sit in city traffic daily, it's worth a few percent — which on a car burning $2,611 of fuel a year is real, if not dramatic. We put those annual fuel figures by fuel type in context separately.

And as always, check what's open on the specific car: some start-stop systems have been subject to recalls for restart failures in traffic, which is exactly the sort of campaign a second owner never hears about. A free VIN check shows what's outstanding.