Updated: 20 September 2026 la 12:08. Articolul a fost revizuit pentru a reflecta informațiile disponibile la această dată.
A car with a flat 12 V battery can be jump-started with another vehicle and jumper cables, but only if the battery is not damaged and the location is safe. The correct order is: red to the positive terminal of the flat-battery vehicle, red to the positive terminal of the assisting vehicle, black to the negative terminal of the assisting vehicle, then black to the designated ground point on the flat-battery vehicle. As a rule, the final clamp should not be attached to the negative terminal of the flat battery.
Before doing anything, check your vehicle’s manual. On some models, the battery is not accessible under the bonnet, and the manufacturer provides dedicated jump-start terminals and a ground point. For hybrid and electric vehicles, cables can help only the auxiliary 12 V battery—not the high-voltage battery.
Stop before connecting the cables if you see any of these situations
- The battery is swollen, cracked, leaking or has a strong, pungent smell.
- The car is in a location where you cannot work away from traffic, without adequate visibility or on a dangerous roadway.
- The cables have cut insulation, exposed wires, loose clamps or heavy corrosion.
- You cannot safely identify the terminals or the recommended ground point.
- You are trying to jump-start the traction battery of an electric or hybrid vehicle. Do not do this.
In these cases, roadside assistance is the best option. If you are stranded while travelling to a destination, you can also check traffic conditions in Romania before deciding whether to wait for help in a safe place or move the car after it starts.
To complement the information above, see How to calculate the real cost of a car journey in Romania: fuel, vignette and bridge tolls, which explores an aspect directly related to this topic.
What you need
- A set of jumper cables in good condition.
- A second vehicle with a 12 V electrical system and a working battery, or a portable jump starter compatible with your vehicle.
- Your vehicle’s owner’s manual, in print or on your phone, especially if the battery is not in the engine compartment.
- Ideally, gloves and safety glasses.
Do not let the two vehicles touch. Put automatic transmissions in Park and manual transmissions in neutral; apply the parking brake and switch off unnecessary electrical loads: lights, climate control, radio and chargers.
The order of the four clamps: the procedure for a standard 12 V car
Unless the manual specifies a different setup, connect the cables with both engines switched off.
- Red to the positive (+) terminal of the flat battery. Identify the terminal marked “+” or the red cover. If the vehicle has a dedicated positive terminal under the bonnet, use that.
- The other red clamp to the positive (+) terminal of the good battery.
- Black to the negative (−) terminal of the good battery.
- The other black clamp to the ground point on the flat-battery vehicle. Choose the point indicated in the manual. If none is marked, manufacturers’ manuals generally use a solid, unpainted metal part away from the battery and fuel-system components.
This sequence keeps any spark from the final connection away from the battery. The Ford Transit manual, for example, explicitly specifies a positive terminal and a ground point, and warns against attaching the negative cable anywhere other than the designated ground. Ford’s jump-starting instructions illustrate this order.
Do not allow the clamps to touch each other once one of them is already connected. Keep the cables away from fans, belts, pulleys and other parts that may move when the engine starts.
After connecting: when to try starting
Give priority to the manual of the assisting vehicle. Instructions vary between models: some recommend starting the donor vehicle’s engine and letting it run for a few minutes before attempting to start the other vehicle, while for certain modern systems the manufacturer may require its own procedure.
As a practical rule, start the vehicle providing power only if its manual allows it, let it run briefly, then try the vehicle with the flat battery. Do not keep cranking the starter: a long attempt can overheat components. If the engine does not start after one or two short attempts, stop the procedure and check the connections. If it still does not start, the cause may be a battery with a faulty cell, the alternator, the starter motor, a fuse or another electrical fault.
AAA recommends checking for similar voltages, inspecting the cables and keeping the vehicles separate; it also stresses that damaged or nearly completely discharged batteries may not respond to the procedure. AAA’s guide to using jumper cables provides the same safety guidance.
How to remove the cables after the engine starts
Disconnect them in the reverse order of connection. Do not let the clamps touch.
- Remove the black clamp from the ground point on the vehicle that has started.
- Remove the other black clamp from the battery of the assisting vehicle.
- Remove the red clamp from the battery of the assisting vehicle.
- Remove the final red clamp from the vehicle that had the flat battery.
Afterwards, do not assume the problem is solved simply because the engine is running. A jump-start is a temporary solution. Drive the car or let it run only for as long as the manual recommends, then arrange to have the battery and charging system checked. A battery that repeatedly goes flat may be worn out, but there may also be abnormal electrical drain while the car is parked. For the difference between the two situations, see InfoBuz’s explanation of a battery that goes flat overnight and hidden electrical drains.
Hybrid, plug-in hybrid or electric: what changes
Never connect cables to orange components or to the high-voltage battery. A hybrid usually also has an auxiliary 12 V battery, and that may be the one that is flat. Some models allow the system to be started through a dedicated 12 V terminal, but its location and the steps vary from one model to another.
Toyota manuals clearly distinguish between the 12 V battery and the traction battery: for some hybrids, a flat auxiliary battery can be assisted by another 12 V system, but the traction battery is not handled through this procedure. Toyota documentation for a hybrid model shows why this distinction matters.
| Vehicle type | What you can do | What to avoid |
|---|---|---|
| Conventional 12 V car | Use cables in the order positive, positive, negative, ground. | Do not attach the final clamp to a terminal chosen at random. |
| Hybrid / plug-in hybrid | Check the manual for the 12 V terminal and ground point. | Do not touch the traction battery or orange cables. |
| Electric vehicle | Use only the points and method specified by the manufacturer for the auxiliary 12 V battery. | Do not try to “charge” the propulsion battery with cables. |
Mistakes that can turn a flat battery into a bigger problem
- Reversing polarity: red to positive, black to negative; check twice before making the final connection.
- Using a battery with a different nominal voltage.
- Connecting the final black clamp directly to the negative terminal of the flat battery when the vehicle has a dedicated ground point.
- Working near a flame, cigarette or source of sparks.
- Persisting repeatedly when the engine will not start. Cables do not repair a faulty starter motor, a failed alternator or a battery with internal damage.
- Push-starting a modern car without checking the manual. Many automatic, hybrid and electric vehicles must not be started this way.
If the battery failed on a cold day, after very short trips or after the car had been parked for a long time, the cause may be temporary. If it happens again, have the battery and alternator checked before your next longer journey.
Frequently asked questions
In what order should jumper cables be connected?
Red to the positive terminal of the vehicle with the flat battery, red to the positive terminal of the good battery, black to the negative terminal of the good battery, then black to the designated ground point on the vehicle with the flat battery.
Why should the final black cable not be connected to the negative terminal of the flat battery?
The final connection can produce a spark. A ground point away from the battery reduces the risk of this happening near a battery that may give off flammable gases. If the manual specifies a ground point, it takes priority.
How long should you let a car run after a jump-start?
There is no universally valid time period. Follow the vehicle manual and arrange testing of the battery and alternator. If the battery goes flat again, simply running the engine will not resolve the cause.
Can you jump-start a hybrid car?
Some hybrids allow the auxiliary 12 V battery to be temporarily powered through dedicated points. Do not use cables on the traction battery or orange cables; consult the manual for your model.
