Roadside assistance

The battery, the first cause of a breakdown

Nearly half of all roadside call-outs involve the battery, and the proportion climbs higher still in December and January: cold reduces the available capacity at exactly the moment the starter, the heating and the headlights are asking for most. A battery that struggles to start in November almost always leaves its owner stranded in January.

A self-contained booster replaces the second car and the cables. It fits in the glovebox, recharges over USB and doubles as a power bank.

Choosing the amperage

• Up to 2.0 L petrol : 400 to 600 A is plenty, cold weather included.
• Diesel up to 2.5 L : aim for 600 A as a minimum, a diesel starter asks for more when cold because of the compression.
• Beyond that, large diesels and vans : you need to go up to 1,000 A and beyond.

Two figures deserve to be told apart. The peak current, the one pushed on the packaging, lasts only a fraction of a second; the cranking current, which is lower, is the one that actually counts. And a booster is recharged two or three times a year even when unused: a unit left in the boot for two winters is flat on the day you need it.

Tyre pressure: what neglecting it costs you

A tyre 0.5 bar under-inflated increases fuel consumption by about 2.5%, lengthens the braking distance and wears faster on the shoulders. Pressure is checked cold, on tyres that have not run more than a few kilometres: measured after an hour on the motorway, it reads about 0.3 bar high.

A cordless inflator with automatic stop handles the everyday case — checking and adjusting every month without queuing at the petrol station. Allow one to two minutes per tyre for an adjustment, longer for a flat tyre, and check that the figure shown matches the one on the label in the door pillar, which often differs between front and rear.

One device or two

A booster with a built-in compressor covers both failures in a single unit and saves charging two devices. It is bulkier and heavier than a booster alone. If the car stays in town with petrol stations nearby, a compact booster is enough; for long journeys, the countryside or a vehicle that sleeps outside, the combined version is the better compromise.

The questions we get asked

How powerful a booster do I need for my car?

400 to 600 A for a petrol engine up to 2.0 L, at least 600 A for a diesel up to 2.5 L, 1,000 A and above beyond that. A diesel asks for more when cold because of its compression.

Can a booster stay in the boot permanently?

Yes, provided you recharge it two or three times a year even without using it. A lithium battery slowly discharges on its own: a booster forgotten for two winters is flat on the day you break down.

When should you check your tyre pressure?

Cold, before you have driven more than a few kilometres. Measured after a journey, the pressure reads about 0.3 bar high, which leads to under-inflating.