Jump starters and jumper cables: choose and use them safely, even on hybrids and EVs
Where each clamp goes, why battery gas is dangerous and how to store a jump pack
Safety Behind the Wheel Foundation built this guide from National Highway Traffic Safety Administration (NHTSA) guidance, Occupational Safety and Health Administration (OSHA) battery rules and guidance, the Centers for Disease Control and Prevention (CDC), federal vehicle safety standards and published eye injury research. Every source is listed at the end.
What jump starters and jumper cables do
Nearly every car and light truck has a low voltage battery, usually 12 volts. Hybrids and electric vehicles have one too. In a gas or diesel vehicle, it powers the starter motor. In a hybrid or electric vehicle, it runs the lights and instruments [1]. If it dies, the vehicle may not switch on.
Two tools can lend that battery enough power for one start. Jumper cables, also called booster cables, are two insulated wires with clamps. They borrow power from a second vehicle. A portable jump starter, or jump pack, is a battery in a case with short cables attached. It needs no second car.
Both are emergency readiness gear. NHTSA lists jumper cables among the winter supplies to carry [5]. It also notes that battery power drops in the cold, while gas and diesel engines need more power to start [5].
Drivers and families keep them so a dead battery is a short delay. Parents may want a new driver to have a way home without relying on a stranger. Fleets use them to keep crews moving. Remote travelers carry them where help may be hours away.
You can buy both at auto parts stores, outdoor and camping retailers, hardware and warehouse stores, and fleet or safety suppliers. The dealer’s parts department can say what the maker suggests for your model.
When a jump start makes sense, and when it does not
Ask two questions first. Is this a safe place to work? Is the battery really the problem?
A jump start means standing at an open hood, often between two vehicles. That is fine in a driveway or quiet parking lot. On a highway shoulder, it puts you beside traffic. There, protect yourself first and call for roadside help. Our roadside breakdown safety guide covers where to stop and whether to stay in the car.
Signs of a weak battery include rapid clicking, dim dash lights and slow cranking. Lights left on or weeks without driving can drain a battery. If the engine cranks at normal speed but will not run, look elsewhere. If the battery warning light came on while driving, the charging system may be failing. A jump might get you going, but the vehicle could stall again in traffic.
Skip the jump and call for help when:
- The battery case is cracked, swollen or leaking.
- The vehicle was just in a collision or sat in floodwater.
- The cables have cracked insulation or bare wire.
- You cannot find the correct terminals in the manual.
- The two vehicles use different system voltages.
After a collision, NHTSA advises treating a damaged high voltage battery as live and fully charged [1]. See our guide on electric vehicles after a serious crash.
Why battery work calls for care: gas, sparks and acid
The common car battery is a lead acid battery, which contains sulfuric acid. It can give off a mix of hydrogen and oxygen gas. A 1982 review of eye injuries from battery explosions traced the blasts to that gas igniting [2].
The harm can be serious. One review of 93 battery related eye injuries at a single medical center found most were minor. Still, 9 patients, or 10%, had lasting eye damage or needed a hospital stay [3]. Explosions caused all of the severe injuries [3]. Another clinic saw 62 patients with eye injuries from battery explosions in eight months [6].
These studies are decades old, but the hazard remains. Where forklift and other industrial truck batteries are charged, OSHA still requires ventilation to clear the gas. It bans smoking there and requires steps to prevent sparks and flames. It also says tools and metal objects must be kept off the tops of uncovered batteries [7].
The acid is a second hazard. NIOSH lists eye and skin burns among the effects of sulfuric acid. Its first aid advice is to flush the eyes or skin with water right away [8]. Then get medical care.
So put on safety glasses before opening the hood. The authors of a 2015 case report urged people to treat any battery as a possible explosive and to wear protective gear around one [9]. Safety Behind the Wheel Foundation gives drivers the same advice. Gloves help too. Take off rings and watches, since metal across the terminals can heat up fast.
Jumper cables or a portable jump starter?
Each tool has its place, and some drivers carry both.
Comparison compiled by Safety Behind the Wheel Foundation
Jumper cables vs. a portable jump starter
| Question | Jumper cables | Portable jump starter |
|---|---|---|
| Needs a second vehicle? | Yes | No |
| Needs charging? | No | Yes, on a schedule |
| Works in a tight spot? | Only if cars can park close | Yes |
| Shelf life | Many years if kept dry | Battery wears out |
| Extra risk | Wrong hookup between cars | Lithium battery heat or damage [4] |
If you often drive alone, at night or far from town, a pack means no waiting for a stranger. If you want something that never needs charging, cables are simpler.
Choosing equipment that fits your vehicle
Start with the owner’s manual. It shows where the battery or jump terminals are and lists any jump start warnings.
Jumper cables
- Length. Longer cables help when cars cannot park nose to nose, or when the battery is in the trunk.
- Thickness. Thicker wire carries current with less heat. A smaller gauge number means a thicker wire.
- Clamps. Look for strong springs, firm jaws and plastic covered handles.
- Storage. A bag keeps the set together and the clamps off other metal.
Portable jump starters
- Voltage. Most cars and light trucks use 12 volts. Some heavy trucks use other voltages, so match the pack to the vehicle.
- Engine fit. Packs are rated for certain engine sizes and fuel types. Larger engines and diesels may need a stronger pack. “Peak amp” numbers are hard to compare, so go by the maker’s engine guidance.
- Protection. Look for protection against reversed clamps, short circuits and overheating.
- Safety testing. OSHA advises that lithium batteries and chargers be tested to a recognized standard and, where it applies, certified by a Nationally Recognized Testing Laboratory [4]. Look for that kind of listing mark.
A built in flashlight or USB port is handy, but it should not drive the choice.
Hybrids and electric vehicles: what changes
Hybrids and electric vehicles have two electrical systems. A high voltage battery drives the motor. A 12 volt battery runs the lights and instruments [1]. Federal safety standards treat parts of the electric drive system above 60 volts of direct current as high voltage. High voltage cables outside protective covers must have orange outer coverings [10].
NHTSA is clear on the key point. The high voltage battery cannot be jumped. In most cases the 12 volt battery can be, much as in a gas car [1].
Comparison compiled by Safety Behind the Wheel Foundation
What a jump can help, by vehicle type
On a hybrid or electric vehicle, check four things:
- Jump points. The 12 volt battery may sit in the trunk, under a seat or behind a panel. Some vehicles have jump posts under the hood. NHTSA tells owners to check the manual for the battery’s location and jump steps [1].
- Giving a jump. Some manuals warn against using a hybrid or electric vehicle to start another car. Check before you offer.
- Fully off. Many of these vehicles are silent when on, so confirm the power is off.
- Orange cables. Keep hands off them. Clamp only where the manual says.
Some newer electric vehicles use a low voltage battery with a different voltage or chemistry. Their manuals may give special steps or say to call for service. A jump will not add driving range. A low high voltage battery needs a charger.
Our electric and hybrid vehicle safety guide explains what a dead 12 volt battery can do to door buttons and screens.
How to jump start with cables, step by step
This is the common order. If your manual differs, follow the manual.
- Park the good vehicle close without touching. Set both parking brakes and shift into Park or Neutral.
- Turn off both vehicles and their lights, fans and radios.
- Put on safety glasses and gloves. If the dead battery is cracked, swollen or leaking, stop.
- Find the positive (+) and negative (-) terminals or jump posts on both vehicles.
- Clamp red to the positive terminal of the dead battery.
- Clamp the other red end to the positive terminal of the good battery.
- Clamp black to the negative terminal of the good battery.
- Clamp the last black end to bare, unpainted metal on the stalled vehicle, away from the battery. Use the manual’s ground point if it has one.
- Start the good vehicle and let it run a few minutes.
- Start the stalled vehicle. After a few short tries with no luck, stop and call for help.
- Remove clamps in reverse order, starting with the ground point. Keep the clamps from touching.
Step 8 matters most. The final connection is the one most likely to spark. Making it away from the battery keeps that spark away from battery gas [2].
How to use a portable jump starter
Packs differ, so follow the pack’s own instructions. The usual routine:
- Check that the pack is charged and its clamps are in good shape.
- With the vehicle and pack both off, clamp red to the positive terminal or jump post.
- Clamp black to the ground point or negative terminal the manual names.
- Switch on the pack, then start the vehicle.
- Switch off the pack. Remove the black clamp, then the red.
- Recharge the pack soon.
If the pack or its cables get hot, stop and let them cool.
After the engine starts
A jump start is a bridge, not a repair. A battery that died once may die again.
Run or drive the vehicle as long as the manual suggests so the battery can recharge. Then have the battery and charging system tested. NHTSA suggests a mechanic check them before winter [5].
Watch where the engine runs. CDC says a vehicle should never run inside a garage attached to a home, and an open door does not make it safe [11]. If a gas vehicle dies in an attached garage, push it out with help or call a roadside service first.
Storing and maintaining your kit
Cables need little care. Jump starters need a routine.
Many packs use lithium batteries. OSHA guidance on small lithium devices says damage can occur above about 130°F, and that charging lithium ion batteries below freezing can harm them [4]. Parked cars get hot. In one Arizona study on hot days, cabin air in closed vehicles averaged about 118°F (47.6°C) in the sun [12]. Keep the pack out of direct sun and follow the maker’s storage range.
OSHA also advises cool, dry storage and chargers made for the device. Unplug once fully charged. Before each use, look and listen for warning signs: a bulging or cracked case, hissing, leaks, heat or smoke [4]. A pack with any of those signs should come out of service and be kept away from anything that can burn [4]. Ask your local waste agency how to dispose of it.
Check your vehicle for open recalls with NHTSA’s recall tool, which also covers tires, car seats and other equipment [13]. Register your jump starter with its maker to get any safety notice.
Frequently asked questions
Can a car battery give me an electric shock?
A 12 volt battery is unlikely to shock you through dry skin. The bigger dangers are sparks, gas and acid. Lead acid batteries can release a hydrogen and oxygen mix that can ignite [2]. A wrench or ring that touches both terminals can heat up and burn you. Hybrids and electric vehicles are different. Never touch their orange cables or the high voltage battery [10].
Can I use my hybrid or electric vehicle to jump another car?
It depends on the vehicle. Some manuals allow it with limits, and some warn against it. Read the jump start section of your manual before you offer help. If the manual says no, a portable jump starter lets you help without risking your own vehicle’s electronics.
Can a jump starter charge an electric vehicle’s main battery?
No. NHTSA says the high voltage battery in an electric or hybrid vehicle cannot be jumped [1]. A pack can only help the 12 volt battery so the vehicle can switch on. A low main battery needs a charger or a tow. Towing takes care, since towing on the drive wheels can damage these vehicles [1].
Is it safe to keep a jump starter in my car all year?
Many people do, but heat and cold matter. OSHA says lithium batteries can be damaged above about 130°F, and charging below freezing can harm lithium ion cells [4]. Cabin air in sunny parked cars averaged about 118°F in one Arizona study [12]. Keep the pack out of direct sun, follow the maker’s temperature range, and charge it indoors in winter.
What if the vehicle still will not start after a jump?
Stop after a few short tries. Long cranking can overheat the starter and drain the good battery or pack. Clicking with a good connection may mean a bad battery, a loose cable or a starter problem. If the engine cranks normally but will not run, the battery is probably not the cause. Call a roadside service or a mechanic.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges drivers to jump a battery only in a safe spot, with eye protection on and the owner’s manual in hand. Jumper cables and jump starters can turn a dead battery into a short delay. Used carelessly, they expose you to battery gas, acid and traffic. The safe routine stays the same: pick a safe spot, protect your eyes, follow the manual and make the last connection away from the battery.
Hybrids and electric vehicles add one rule. Only the 12 volt battery gets a jump, and orange high voltage parts are off limits. Keep your kit charged and checked, and get the battery tested after any jump.
Related articles
- Roadside breakdown safety: what to do when your car breaks down
- Electric and hybrid vehicle safety: a practical guide for families
- What to do with an electric vehicle after a serious crash
- Vehicle maintenance for safety: tires, brakes, lights and warning signs
- Driving in snow and ice: grip, black ice, skids and when to stay home
Sources and further reading
- 1National Highway Traffic Safety Administration. Electric and Hybrid Vehicles: Battery, Charging & Safety. Accessed October 2026. nhtsa.gov/…/electric-and-hybrid-vehicles
- 2Siebert S. Ocular trauma from lead-acid vehicle battery explosions. Australian Journal of Ophthalmology, 1982;10(1):53-61 (via PubMed, PMID 7103864). Data year: case series from Adelaide teaching hospitals, published 1982 (case years not stated in abstract). pubmed.ncbi.nlm.nih.gov/7103864
- 3Holekamp TL. Ocular injuries from automobile batteries. Transactions of the Section on Ophthalmology, American Academy of Ophthalmology and Otolaryngology, 1977;83(5):805-10 (via PubMed, PMID 929798). Data year: 93 cases over 8.5 years, published 1977 (exact years not stated in abstract). pubmed.ncbi.nlm.nih.gov/929798
- 4Occupational Safety and Health Administration. Preventing Fire and/or Explosion Injury from Small and Wearable Lithium Battery Powered Devices. Safety and Health Information Bulletin SHIB 06-20-2019, published June 2019. osha.gov/…/shib011819.pdf
- 5National Highway Traffic Safety Administration. Winter Weather Driving Tips: Prepare Your Vehicle. Accessed October 2026. nhtsa.gov/winter-driving-tips
- 6Minatoya HK. Eye injuries from exploding car batteries. Archives of Ophthalmology, 1978;96(3):477-81 (via PubMed, PMID 564686; doi:10.1001/archopht.1978.03910050253012). Data year: eight consecutive months of clinic cases, published 1978 (months not stated in abstract). pubmed.ncbi.nlm.nih.gov/564686
- 7Electronic Code of Federal Regulations. 29 CFR 1910.178(g), Powered industrial trucks: Changing and charging storage batteries. Up to date as of October 1, 2026. ecfr.gov/…/section-1910.178
- 8National Institute for Occupational Safety and Health. NIOSH Pocket Guide to Chemical Hazards: Sulfuric acid. Accessed October 2026. cdc.gov/niosh/npg/npgd0577.html
- 9Görgülü T, Torun M, Olgun A. A cause of severe thigh injury: Battery explosion. Annals of Medicine and Surgery, 2016;5:49-51, published online December 2015 (via PubMed, PMID 26862395; doi:10.1016/j.amsu.2015.12.048). pubmed.ncbi.nlm.nih.gov/26862395
- 10Electronic Code of Federal Regulations. 49 CFR 571.305a, Standard No. 305a; Electric powertrain integrity. Up to date as of October 1, 2026. ecfr.gov/…/section-571.305a
- 11Centers for Disease Control and Prevention. Carbon Monoxide Poisoning Basics. Updated January 12, 2026. cdc.gov/carbon-monoxide/about/index.html
- 12Vanos JK, Middel A, Poletti MN, Selover NJ. Evaluating the impact of solar radiation on pediatric heat balance within enclosed, hot vehicles. Temperature, 2018;5(3):276-292 (via PubMed, PMID 30377643; doi:10.1080/23328940.2018.1468205). Data year: field measurements in Tempe, Arizona, published 2018. pubmed.ncbi.nlm.nih.gov/30377643
- 13National Highway Traffic Safety Administration. Check for Recalls: Vehicle, Car Seat, Tire, Equipment. Accessed October 2026. nhtsa.gov/recalls
This article reflects the safety priorities of roadside emergency readiness and safe battery handling. It is general safety education, not legal, medical or insurance advice, and it does not replace your owner's manual. Rules change, so verify details with official sources. For your own vehicle, contact the dealer's service department or a qualified mechanic. For a damaged hybrid or electric vehicle, contact the maker or a trained service shop. For an acid injury, seek medical care. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Jump starters and jumper cables: choose and use them safely, even on hybrids and EVs.” drivewithcare.org, https://drivewithcare.org/jump-starter-jumper-cables-safe-use/. Reviewed October 2026.
Special thanks to our contributors
We appreciate the professionals, experts, and community members who share their knowledge and perspectives to help make this resource better. Your insights are always welcome and appreciated.
Have professional expertise, firsthand experience, or a perspective that could make this resource better?
We welcome your input. Your knowledge and experience can help us make this resource more useful, accurate, and meaningful to the people who rely on it.
Thank you. Your contribution is on its way.
We’re grateful you took the time to share your knowledge with us. Our team reviews every contribution with care. If it helps improve this resource, we’ll update the page and recognize you the way you chose.
Keep learning
Safe Driving Resource Center
Guides, self-checks and articles for drivers, parents of new drivers, and families recovering after a crash.
