Jump starting 2026 – safely and reliably to your destination
A flat car battery can happen to anyone – on a cold winter morning, after a long period of standing or simply due to a forgotten consumer. Anyone who then knows how to jump start correctly not only saves time and nerves, but also protects sensitive vehicle electronics and AGM or EFB batteries. In this updated 2026 guide, we show the exact order, explain the ADAC costs and give you a detailed comparison between classic jump starting and modern lithium jump starters (boosters).
The correct order is crucial: an incorrect cable connection can not only lead to violent sparks and oxyhydrogen explosions, but also destroy sensitive control units – damage that can quickly run into four figures. With our step-by-step instructions, real technical values on currents (CCA), voltages (V) and capacities (Ah) and a well thought-out FAQ section, you are prepared for any breakdown situation.
By the way: a high-quality 12-volt battery is recognisable by stable CCA values and a good reserve capacity – more on this in our guide.
The correct order when jump starting: success in 6 steps
This procedure applies both to conventional starter batteries and to modern AGM and EFB batteries, such as those fitted in vehicles with a start-stop system. Follow the sequence strictly – this minimises the risk of voltage spikes and damage to the vehicle electronics.
Step 1: Safety first – preparation and protective equipment
Before you even pick up a cable, the following points should be met:
- Switch off the ignition of both vehicles, deactivate all consumers (lights, ventilation, radio, seat heating).
- Put on safety goggles and protective gloves – battery acid and flying sparks can be dangerous.
- The vehicles must not touch each other – otherwise an unintended current flow can occur.
- Jump leads with a sufficient cross-section: For petrol engines at least 16 mm², for diesel vehicles (especially with a high cold cranking current of 600–800 CCA) 25 mm² or more is recommended.
- No visible damage to the battery casing – if there are cracks or leaking acid, do not jump start.
Step 2: Position the vehicles and open the bonnets
Park the donor vehicle so that the jump leads can comfortably reach both batteries without being under tension. Both engines remain off.
Step 3: Positive cable first – red to positive of the full battery, then to positive of the flat battery
Connect the red cable to the positive terminal (+) of the full (donor) battery. Then connect the other end to the positive terminal (+) of the discharged battery. Make sure the terminal clamps are secure – a loose connection can cause sparks and voltage spikes.
Step 4: Negative cable to the negative terminal of the full battery
Take the black cable and attach it first to the negative terminal (−) of the donor battery.
Step 5: Negative cable to the earth point of the broken-down vehicle – not directly to the negative terminal!
The last connection is the crucial safety step: clamp the free end of the black cable to a bare, unpainted metal point in the engine compartment of the broken-down vehicle – a so-called earth point (e.g. engine block or a sturdy bracket). Never clamp directly to the negative terminal of the flat battery. Reason: with a defective or deeply discharged battery, highly flammable oxyhydrogen gas (hydrogen-oxygen mixture) may have formed – a spark at the terminal would trigger an explosion.
Mnemonic: Positive-positive, negative (donor) – earth (recipient).
Step 6: Start the donor, then the recipient – and after a successful start, disconnect in reverse order
Start the engine of the donor vehicle and let it run slightly fast at idle for 2–3 minutes (not full throttle). This allows sufficient charging current to flow into the flat battery. Then try to start the broken-down vehicle. Once it is running, disconnect the cables in exactly the reverse order: First the black cable from the earth point, then from the negative terminal of the donor, then red from the positive terminal of the broken-down vehicle, finally red from the positive terminal of the donor. Let the engine run for at least 20–30 minutes or drive, so that the alternator recharges the battery.
Why this order is so important – technical background
The final earth connection away from the battery not only prevents oxyhydrogen explosions but also reduces voltage spikes on the sensitive CAN bus systems. Modern vehicles with AGM batteries or EFB batteries usually have a battery management system (BMS) that continuously monitors voltage and current. A direct negative connection to the flat battery could “confuse” the BMS with incorrect readings and, in the worst case, lead to charging errors or control unit failures. The voltage in the vehicle electrical system should not drop below 10 V during the starting process; an intact donor with a 12 V battery of 60–100 Ah and a cold cranking current of 500–800 CCA generally provides sufficient reserve.
A typical diesel car requires short-term currents of 600–800 A for a cold start, a petrol engine usually 350–500 A. Therefore, the jump leads must be low-resistance and thick enough – a 10 mm² cable quickly becomes hot and fails at such currents.
ADAC jump start: costs, waiting time and what you need to know
In Germany, the ADAC is the first point of contact when your own battery fails. For ADAC members, the classic on-site jump start is included in the membership fee – so there are no additional costs. Most breakdown insurance policies also cover roadside assistance.
For non-members, the ADAC (or the respective breakdown service) usually charges a call-out flat rate. Often a call-out fee plus a per-minute or fixed price for the jump-start itself is charged. Comparatively cheap is to have a high-quality jump lead or a lithium booster on board yourself and to get help from another driver in the event of a breakdown.
In addition, you should factor in the typical waiting time: depending on how busy the breakdown service is and your location, it can take 30–90 minutes for help to arrive. Especially in winter or on public holidays, longer waiting times occur.
Comparison: classic jump-start (cable + donor vehicle) vs. mobile lithium jump-starter booster
Lithium jump-starter devices have revolutionised breakdown assistance – they are compact, powerful and do not require a second vehicle. But both methods have their advantages and disadvantages, which we compare in the following table:
| Criterion | Jump lead + donor vehicle | Mobile lithium booster |
|---|---|---|
| Dependence on outside help | A second, working vehicle is absolutely necessary | Completely self-sufficient – no donor vehicle required |
| Readiness for use | Ready for use at any time, provided a donor is available | Must be charged regularly (note self-discharge); in cold weather the capacity can decrease |
| Peak current / CCA | Depends on donor battery and cable cross-section; usually 500–800 A without problems | Smaller devices approx. 400–600 A peak, powerful models up to 2000 A (can also start large diesels) |
| Jump-start with flat batteries below 8 V | Usually unproblematic, as the donor battery supplies a stable voltage | Some boosters refuse to work if the residual voltage is too low; high-end devices have a “bypass mode” |
| Risk of error (reverse polarity) | High – incorrect order or swapped poles can cause severe electronic damage | Low – many boosters have reverse polarity protection and acoustic/visual warnings |
| Additional functions | None | Often integrated power bank (USB-A/C), LED torch, emergency light, voltage display |
| Weight and storage space | Approx. 1–2 kg, can be stored flexibly | 0.5–2 kg, usually in a compact bag with accessories |
For people who travel a lot or live in remote areas, a mobile booster is a worthwhile investment. When buying, be sure to check the specified peak amps and the recommended maximum engine displacement or diesel class. A device with 600 A peak confidently starts a 2.0-litre petrol engine, but for a 3.0-litre diesel the booster should be able to deliver at least 1000 A peak.
Typical mistakes when jump-starting and how to avoid them
- Negative terminal directly to the flat battery: Risk of explosion from oxyhydrogen – always connect the black cable to a ground point.
- Cables too thin: A cross-section below 16 mm² can overheat on diesel vehicles and in extreme cases melt. Minimum cross-section: 16 mm² (petrol), 25 mm² (diesel).
- Jump-start with a deeply discharged or frozen battery: A battery with less than 8 V open-circuit voltage or visible ice crystals must not be jump-started – risk of explosion and acid leakage.
- Running the donor vehicle's engine at high revs: Modern alternators supply enough current even at idle; excessive revs can cause voltage spikes and damage sensitive control units.
- Switching on all consumers immediately after a successful start: Let the engine run for a few minutes before activating lights, heating or seat heating so that the battery can build up a basic charge.
- Poor care after jump-starting: A battery that is only minimally charged sulphates faster and permanently loses capacity. After jump-starting, always fully charge with an external charger.
Jump-starting modern vehicles with AGM, EFB and lithium batteries
Vehicles with start-stop automatic systems rely on cycle-resistant AGM or EFB batteries. These are more robust against deep discharge, but do not tolerate improper external power supply. The integrated battery management system (BMS) expects a defined charging voltage and temperature compensation for every charging process. When jump-starting, the donor battery should have a similar voltage level (ideally also AGM). However, conventional flooded batteries are also suitable as long as you observe the correct order and the on-board voltage does not exceed 15 V. You can read more about the properties of AGM batteries in our AGM battery guide.
Lithium starter batteries (LiFePO4) are still rare in passenger cars, but they do appear in lightweight sports cars or as an auxiliary battery. Jump starting can be problematic here – a lithium booster with a suitable charging profile is then the first choice. Jump starting from a lead-acid donor battery should only be done in absolute emergencies with a brief 12 V connection and strict observance of polarity.
After jump starting: charging the battery correctly and protecting it in the long term
A single jump start draws even more capacity from the already weakened battery. If you only drive for 10 minutes to work after jump starting, the battery is not sufficiently charged. The result: sulphation, irreversible capacity loss and the next starting attempt fails the very next morning. We recommend connecting the battery to a mains socket with an intelligent trickle charger after every jump start. Particularly for AGM and EFB batteries, a charger with an IU0U characteristic and temperature sensor is advisable – it prevents overcharging and is gentle on the sensitive fleece material. We explain which charger is optimal for your battery in the 12V battery charging guide. For continuous charging and maintenance of AGM models, we refer to our trickle charger test.
If, after a full charge, the battery does not reach the recommended resting voltage values (12.6–12.8 V) or drops below 10 V under load, replacement is advisable. In the 12-volt battery guide you will find all the criteria for selecting the right starter battery – from capacity (Ah) and cold cranking current (CCA) to dimensions and terminal arrangement.
FAQ – Common questions about jump starting
1. What order must I follow when jump starting?
First the red positive cable: positive terminal of the donor vehicle → positive terminal of the broken-down vehicle. Then the black negative cable: negative terminal of the donor vehicle → earth point (bare metal) on the broken-down vehicle. After starting, disconnect in reverse order: earth point first, then negative terminal of the donor, then positive terminal of the broken-down vehicle, and finally positive terminal of the donor.
2. Why must the negative cable not be connected directly to the negative terminal of the flat battery?
During charging or discharging, highly flammable oxyhydrogen gas can accumulate around the battery. A spark when connecting directly to the negative terminal can ignite this gas and lead to an explosive deflagration with acid splashes. The earth point away from the battery keeps the ignition spark away from the gas.
3. What does jump starting by the ADAC or other breakdown services cost me?
For ADAC members, breakdown assistance and jump starting are usually free of charge. The exact amount depends on the provider, the region and the time of day. It is cheaper to have suitable jump leads or a mobile booster on board yourself and to get help from another road user.
4. Can I jump start any car – even with an AGM or EFB battery?
In principle, yes. However, it is important to use a donor battery that supplies a stable 12 V voltage and – if possible – is of the same type (i.e. AGM to AGM) so as not to confuse the battery management system. Jump starting with chargers in boost mode without sufficient filtering is not advisable, as voltage spikes can damage the control units.
5. What cross-section should jump leads have?
For petrol engines, at least 16 mm² is recommended, preferably 25 mm². For diesel vehicles, especially with a large displacement or high compression ratio, you should use 25 mm² or 35 mm². Too thin a cross-section increases the internal resistance, leads to heat build-up and prevents sufficient current from flowing – starting will then fail despite the donor vehicle.
6. Is it permissible to jump start an electric car or hybrid?
Most electric and hybrid vehicles have a conventional 12 V on-board battery that may be jump started if deeply discharged. The high-voltage battery remains unaffected. Always observe the instructions in the vehicle's operating manual. Many manufacturers recommend that, at least for an electric car, it should only serve as a donor vehicle, not as a recipient, as the DC-DC converters can be sensitive. A mobile lithium booster is usually the safer choice here.
7. What minimum capacity does a lithium jump starter need?
For the average passenger car (up to 2.0 l displacement), a booster with a peak current of 400–600 A and a capacity of around 10,000–20,000 mAh is sufficient. For larger diesels or SUVs, the device should have at least 1000 A peak and 20,000 mAh. Also look for the specification “starting attempts per charge” – good devices manage up to 20 starts.
8. What to do if the engine immediately stalls again after jump starting?
This can indicate a completely discharged battery (< 8 V) or a faulty alternator. Check that all terminals are clean and tight, repeat the starting attempt and let the donor vehicle run for longer. If the voltage still remains below 12.4 V (with the engine running), the alternator is usually faulty. In that case, only a breakdown service will help.
Your experts for starter batteries and accessories – electronicx
If jump starting is only a short-term solution and the battery needs to be replaced permanently, you have come to the right place. Electronicx GmbH from Cleebronn (Baden-Württemberg) offers a comprehensive range of high-performance AGM, EFB, gel and LiFePO4 batteries as well as matching chargers, jump starters and TPMS sensors.
You can reach us by phone on +49 7135 7194106 or by email at [email protected]. Our company headquarters is exclusively:
electronicx GmbHHindenburgstr. 37A
74389 Cleebronn
Germany
Managing Director: Andreas Emschanow | VAT ID: DE300176428 | HRB 752730 (Stuttgart Local Court)
Feel free to browse our AGM car battery range or discover the full scope of our guides to keep your vehicle electronics in perfect shape.