How to Jump-Start a Car Safely, Leads or a Lithium Pack
A flat battery is fixable at the roadside with jump leads and a donor car, or with a compact lithium jump pack. The connection order is what keeps it safe.
Connect red to the dead battery's positive first, then to the donor's positive. Black goes to the donor's negative, then to a bare metal earth point on the dead car's engine, away from the battery. Disconnect in reverse order.
Jump-starting borrows power from another battery to turn your engine over. Done in the right order it is routine. Done in the wrong order it can spark near a battery that vents flammable gas. This is the safe sequence, plus the jump-pack alternative that skips the second car entirely.
Jump leads with a donor car
Park the donor car close but not touching, then switch both cars off. Connect the red lead to the dead battery's positive terminal, then the other end to the donor's positive. Connect the black lead to the donor's negative terminal, then clamp the other end to a solid, unpainted metal point on the dead car's engine or chassis, away from the battery and any fuel lines. That earth point keeps any spark away from the battery itself. Start the donor car and let it run for a few minutes, then try the dead car. Once it is running, disconnect the leads in the exact reverse order, and keep the leads and your hands clear of fans, belts and pulleys throughout.
Lithium jump packs
A lithium jump pack is a compact booster battery that clamps straight onto the flat battery and starts the car with no second vehicle involved. Most modern packs include polarity and spark protection, so they refuse to deliver power if the clamps are on the wrong terminals. That makes them the easier and safer option for most people. Two things matter in practice. Keep the pack charged, because one that sits flat in the boot for a year will let you down. And check its rated capacity suits your engine, since a small petrol engine needs far less cranking power than a large diesel.
After the start, and when not to jump
Once the car is running, drive a decent distance so the alternator can put charge back in. A short hop to the shops will not do it. A battery that keeps going flat needs a proper health check, because a jump treats the symptom, not the cause. Never jump a battery that is visibly damaged, leaking or frozen. And on cars with stop-start systems or sensitive electronics, check the handbook first. Many specify approved jump points or an earth stud, and connecting anywhere else can upset or damage control modules.
The conditions that matter
- ✓The safe order is positive to positive first, then negative to an earth point on the dead car away from the battery. Disconnect in reverse.
- !Check a jump pack's rated capacity against your engine size, and keep it charged so it works when needed.
- !Never jump a damaged, leaking or frozen battery, and check the handbook on cars with stop-start or sensitive electronics.
General guidance only. Details vary by exact vehicle and change over time; confirm with a reputable specialist before modifying.