To jumpstart a car with another car, use a compatible 12-volt donor vehicle, connect the red positive cable to both positive battery terminals, connect the black cable to the donor negative terminal and an unpainted metal ground on the disabled car, then start the donor and disabled vehicle in that order. The complete process typically takes 10-15 minutes.
Key Facts at a Glance
A conventional gasoline or diesel car normally requires a compatible 12-volt donor system.
The red cable connects positive to positive; the black cable connects donor negative to a metal ground on the disabled vehicle.
The donor engine usually runs for 2-5 minutes before the disabled vehicle attempts to start.
Crank the disabled vehicle for no more than about 5 seconds per attempt, with 30 seconds between attempts.
Remove the cables in reverse order, beginning with the disabled vehicle’s grounding point.
A jumpstart does not repair a failed battery, alternator, starter, or charging system.
What You Need Before Jumpstarting
A safe jumpstart requires two compatible vehicles, a set of insulated jumper cables, and enough access to both batteries or approved remote terminals. The donor vehicle should have a charged battery with the same nominal voltage as the disabled vehicle, which is usually 12 volts for passenger cars, SUVs, and light trucks.
Park the vehicles close enough for the cables to reach without stretching, but prevent the vehicles from touching. Set both transmissions to Park, or Neutral with the parking brake applied for a manual transmission. Switch off headlights, climate control, audio equipment, and other accessories.
Before-Start Checklist
| Requirement | Typical specification | Why it matters |
|---|---|---|
| Donor system voltage | 12 V | Prevents incompatible electrical input |
| Jumper cable length | 10-20 ft | Reaches between parked vehicles |
| Cable thickness | 4- to 8-gauge | Carries high starter current |
| Setup time | 2-4 minutes | Allows inspection and positioning |
| Total procedure | 10-15 minutes | Includes charging and removal |
Do not proceed if either battery is cracked, leaking, swollen, smoking, or covered with heavy corrosion. A frozen lead-acid battery can rupture when charged, so allow it to thaw naturally and inspect it before making a connection.
Do not use a gasoline car to jumpstart an EV unless the EV manufacturer specifically permits it. Many EVs can provide limited 12-volt assistance through an approved terminal, but their high-voltage traction batteries must never be connected to another vehicle.
How Does a Jumpstart Work?
A jumpstart temporarily connects two 12-volt electrical systems in parallel so the donor battery can supply current while the disabled vehicle’s starter motor turns the engine. The alternator does not normally provide the initial starting energy directly; after the engine starts, the alternator restores charge to the vehicle battery.
A starter motor can demand several hundred amperes for a few seconds, particularly in cold weather or with a large diesel engine. Jumper cables reduce voltage loss when they are thick, clean, and fully clamped to suitable metal surfaces.
The connection must preserve polarity. Positive-to-positive and negative-to-ground connections allow current to flow through the disabled vehicle’s normal electrical path, while reversing polarity can damage fuses, control modules, batteries, or alternators.
Which Vehicles Can Be Connected?
| Disabled vehicle | Suitable donor | Main condition |
|---|---|---|
| 12 V gasoline sedan | 12 V gasoline sedan | Donor battery must be charged |
| 12 V SUV | 12 V pickup or SUV | Use heavy-duty cables |
| Diesel truck | Similar-size diesel truck | Small-car cables may overheat |
| Hybrid with 12 V battery | Approved 12 V donor | Follow the hybrid manual |
| Electric vehicle | Manufacturer-approved source | Never connect high-voltage systems |
Always check the owner’s manual first. Some vehicles specify remote positive terminals, prohibit grounding directly to the battery, or require a particular jump-start sequence.
How to Jumpstart a Car With Another Car
Follow these steps in order. The most important success factors are correct polarity, a solid ground connection, and limiting each starting attempt to a few seconds.
Step 1: Position and Secure Both Vehicles
Park the donor vehicle close to the disabled vehicle without allowing the bodies to touch. Put both vehicles in Park or Neutral, apply both parking brakes, and turn both ignitions off.
Open the hoods and locate each battery or the manufacturer-designated jump terminals. Remove plastic covers only where the vehicle manual permits.
You will know it worked when: both batteries or approved terminals are accessible and the cables can reach without tension.
Common mistake: positioning the donor so the cable clamps barely reach, which can pull loose during cranking.
Step 2: Inspect the Batteries and Cables
Check for cracks, leaks, swelling, exposed wires, or severe terminal corrosion. Confirm that both systems are 12 volts and that the cable insulation is intact.
Clean heavy terminal corrosion before connecting if the terminal remains structurally sound. Do not scrape aggressively around a damaged or leaking battery.
You will know it worked when: the terminals are identifiable, dry, and free of conditions that could cause a short or rupture.
Common mistake: attempting to jump a swollen battery because the vehicle appears otherwise normal.
Step 3: Connect the Red Positive Cable
Clamp one red cable end to the positive terminal of the disabled battery. The positive terminal normally carries a plus symbol and may have a red cover.
Connect the other red cable end to the positive terminal of the donor battery. Keep the free black clamps away from both batteries and from body metal while making this connection.
You will know it worked when: both red clamps are firmly attached to positive terminals and cannot rotate off.
Common mistake: relying on terminal color alone instead of confirming the plus symbol or approved positive post.
Step 4: Connect the Black Cable to Ground
Attach one black cable clamp to the donor battery’s negative terminal. Attach the remaining black clamp to a clean, unpainted, heavy metal point on the disabled vehicle’s engine block or chassis, away from the battery and moving belts.
A designated grounding stud is preferable when the manufacturer provides one. Grounding away from the disabled battery can reduce the chance that a spark will ignite hydrogen gas near the battery.
You will know it worked when: the final clamp grips solid metal and does not rest on painted, thin, hot, or moving parts.
Common mistake: attaching the final clamp to the disabled battery’s negative terminal when the manual specifies an engine or chassis ground.
Step 5: Start the Donor Vehicle
Start the donor vehicle and let it run at idle for about 2-5 minutes. Do not repeatedly rev the engine, because high engine speed does not guarantee a safer or faster charge and may stress the charging systems.
The donor battery supplies current while the donor alternator maintains system voltage. A severely discharged battery may need more time, a jump pack, or professional charging instead of repeated cranking.
You will know it worked when: the donor remains running normally and the disabled vehicle’s dashboard lights become brighter or more stable.
Common mistake: immediately cranking the disabled vehicle before allowing a short stabilization period.
Step 6: Start the Disabled Vehicle
Turn the disabled vehicle’s ignition or start control on, then crank for no more than about 5 seconds. If the engine does not start, wait at least 30 seconds before another attempt while checking the clamps.
Try no more than two or three attempts without reassessing the battery, cable quality, fuel supply, immobilizer, starter, and engine condition. A rapid clicking sound often indicates insufficient voltage or poor clamp contact.
You will know it worked when: the engine starts and continues running without the starter motor engaged.
Common mistake: holding the key in the start position for 15-20 seconds, which overheats the starter and cables.
Step 7: Remove the Cables in Reverse Order
Once the disabled engine runs, remove the cables in this order:
- Black clamp from the disabled vehicle’s engine or chassis ground.
- Black clamp from the donor battery’s negative terminal.
- Red clamp from the donor battery’s positive terminal.
- Red clamp from the disabled battery’s positive terminal.
Keep the clamps from touching one another or any metal surface during removal. Close the hoods only after every clamp is disconnected.
You will know it worked when: all four clamps are removed and both engines continue running normally.
Common mistake: removing the positive cable first or allowing a loose clamp to contact the body.
Step 8: Recharge and Test the Disabled Vehicle
Leave the restarted vehicle running for at least 20-30 minutes, or drive it for roughly 20-30 minutes when traffic and vehicle condition make that safe. Driving may restore some charge, but it cannot reliably recharge a deeply discharged or failing battery.
Turn off unnecessary electrical loads during the initial drive. Have the battery and charging system tested soon afterward, especially if the vehicle needed a jump because of an unknown cause.
What If the Car Does Not Start?
A car that does not start after a correct jump connection usually has a deeper problem than a mildly discharged battery. Recheck polarity, clamp contact, grounding location, donor battery condition, and whether the disabled vehicle requires a remote terminal.
| Symptom | Likely cause | Next action |
|---|---|---|
| Rapid clicking | Low voltage or poor clamp contact | Re-seat clamps and wait 5 minutes |
| One heavy click | Starter, cable, or low battery fault | Test voltage and starter circuit |
| No dashboard lights | Disconnected terminal or failed battery | Inspect battery terminals and fuses |
| Engine cranks normally but will not run | Fuel, ignition, immobilizer, or sensor issue | Stop jump attempts and diagnose engine |
| Starts, then dies | Alternator or charging fault | Check charging voltage immediately |
| Cables become hot | Undersized cables or poor connection | Stop, disconnect safely, inspect cables |
A fully charged 12-volt battery commonly measures about 12.6 volts at rest, although temperature and battery condition affect the reading. With the engine running, many conventional vehicles show approximately 13.5-14.8 volts at the battery, but the exact range depends on the vehicle’s smart-charging system. Use the manufacturer’s specification rather than treating these figures as universal.
If sparks occur when making the final connection, stop and verify polarity. A small brief spark can result from vehicle electronics waking up, but sustained sparking, smoke, heat, or a burning smell requires immediate disconnection and professional inspection.
Common Mistakes and How to Fix Them
Connecting Positive and Negative Backward
Reversed polarity can blow fusible links and damage sensitive electronic modules within seconds. Do not continue after a polarity mistake; switch both vehicles off, disconnect the cables, and have the electrical system checked if warning lights or electrical failures appear.
Using a Weak Donor Vehicle
A small donor battery may not provide enough current for a large diesel engine or a deeply discharged SUV battery. Use a donor with a similar or larger engine and heavy-duty cables, or use a portable jump starter rated for the disabled vehicle’s engine size.
Grounding on Painted Metal
Paint and thin sheet metal create high resistance, which reduces available starter current and produces heat at the clamp. Choose a clean, unpainted engine or chassis point specified by the vehicle manufacturer.
Assuming a Jump Fixes the Battery
A jumpstart restores temporary operation, not battery capacity. If the battery is more than about 3-5 years old, repeatedly goes flat, or needs another jump within days, request a battery and charging-system test.
Continuing After a Failure
Repeated long cranking can overheat the starter, cables, and donor system. Stop after two or three short attempts and investigate the cause instead of increasing engine speed or leaving the cables connected indefinitely.
Special Situations and Safer Alternatives
Can You Jumpstart a Hybrid?
A hybrid may be jumpstarted through its 12-volt auxiliary battery or designated terminal, but the procedure varies by model. A hybrid’s high-voltage battery pack is not a substitute for a normal 12-volt jump connection, and exposed orange cables must never be touched.
Use the owner’s manual for Toyota Prius, Ford Escape Hybrid, Hyundai Ioniq, and other models because terminal locations and post-start instructions differ. A hybrid can sometimes provide 12-volt assistance to another vehicle, but manufacturers commonly discourage using it as a donor because the auxiliary system may not be designed for that load.
Can You Jumpstart an Electric Vehicle?
An EV’s high-voltage traction battery must not be connected to another car. Some EVs permit a 12-volt jump through clearly marked service terminals, but the procedure only wakes the vehicle’s low-voltage electronics and does not provide a conventional engine-starting function.
Use the manufacturer’s roadside procedure or call assistance. Never connect jumper cables to orange high-voltage wiring, traction-battery terminals, or unmarked components.
Is a Portable Jump Starter Better?
A portable lithium jump starter is often safer and more convenient when no second car is available, but it must have enough starting-current capacity and a charged internal battery. A jump pack also reduces the risk of connecting two vehicles incorrectly.
| Option | Typical cost | Typical time | Best use |
|---|---|---|---|
| Jumper cables and donor car | $20-$60 for cables | 10-15 minutes | Routine 12 V battery discharge |
| Portable jump starter | $60-$250 | 5-10 minutes | Remote locations or one-car households |
| Roadside assistance | $50-$150 per incident | 30-90 minutes | Unsafe location or uncertain fault |
| Battery replacement | $100-$300 installed | 30-90 minutes | Failed or aged battery |
| Battery charger | $40-$180 | 4-12 hours | Home recharge and diagnosis |
A jump pack is not suitable for a battery that is leaking, swollen, frozen, or physically damaged. Roadside assistance is the better choice on a highway shoulder, in severe weather, or when the vehicle has high-voltage systems and unclear terminals.
Time, Cost, and Equipment Guide
The procedure itself commonly takes 10-15 minutes, while a roadside call may take 30-90 minutes depending on location and demand. Cable quality, battery access, weather, and vehicle design create the largest time differences.
| Situation | Typical time | Typical cost | Recommended approach |
|---|---|---|---|
| Clear battery access, healthy donor | 10-15 minutes | $0-$60 | Standard cable procedure |
| Severe battery discharge | 15-30 minutes | $0-$250 | Longer stabilization or jump pack |
| Damaged or swollen battery | Do not attempt | $100-$300 | Battery replacement or recovery |
| Remote roadside location | 30-90 minutes | $50-$150 | Roadside assistance |
| Repeated battery failure | 1-2 hours | $100-$400 | Battery and charging diagnosis |
What Should You Do After the Engine Starts?
Drive or run the vehicle for approximately 20-30 minutes, then arrange a battery and alternator test rather than assuming the problem is solved. A vehicle that restarts normally after being switched off may still have a battery with insufficient reserve capacity.
Record the circumstances of the failure. Interior lights left on suggest accidental discharge, while repeated overnight discharge points toward parasitic drain, a faulty module, or an aging battery. A battery warning light, dimming headlights, or stalling while driving indicates a charging-system problem that requires prompt attention.
Do not shut the engine off in an isolated location until you know the vehicle can restart. If the battery is old or the engine died while driving, arrange repair or recovery instead of relying on another jump.
Frequently Asked Questions
Can I jumpstart a car while it is raining?
Yes, ordinary rain does not prevent a 12-volt jumpstart when the batteries and terminals are intact, but water must not pool around damaged electrical components. Keep the cable clamps insulated from one another, avoid standing water, and postpone the procedure during lightning or flooding.
Which car do I turn on first?
Start the donor vehicle first and let it idle for approximately 2-5 minutes before trying the disabled vehicle. Starting the disabled vehicle first provides no benefit because its battery is the depleted source. Turn both vehicles off before connecting the cables.
How long should I drive after a jumpstart?
Drive for about 20-30 minutes if the vehicle runs normally, but driving time does not guarantee a full recharge. A deeply discharged battery may require a battery charger, and a failing alternator may leave the vehicle unable to restart after the engine is switched off.
Can jumper cables damage a car?
Jumper cables can damage a car when polarity is reversed, voltage is mismatched, clamps touch, or a damaged battery is charged. Correctly connected 12-volt cables normally do not harm compatible vehicles. Follow the owner’s manual when it specifies remote terminals or a special sequence.
Why does my car need a jump every morning?
A car that needs a jump every morning may have a failed battery, a parasitic electrical drain, a loose connection, or an alternator that is not recharging the battery. Battery age alone does not identify the cause, so request both a battery load test and a charging-system test.
Should I replace the battery after a jumpstart?
Replace the battery when testing shows low capacity, when the battery is swollen or damaged, or when it is typically more than 3-5 years old and repeatedly discharges. A single jump after leaving lights on does not automatically require replacement.
The Bottom Line
To jumpstart a car with another car safely, use compatible 12-volt systems, connect red positive to both positive terminals, connect black from the donor negative terminal to an unpainted ground on the disabled vehicle, wait 2-5 minutes, and crank for no more than about 5 seconds. Remove the cables in reverse order, then test the battery and charging system if the failure repeats.
