Dead car battery in freezing weather: jump start guide¶

A car that clicks, groans, or does nothing at all on a freezing morning is almost always a battery problem. Cold weather thickens engine oil and slows the chemical reaction inside the battery at the same moment the engine needs the most power to turn over. This guide shows you how to jump start a car safely in the cold, how to tell when you should not attempt a jump, and what to do when a jump does not work.

The steps matter because a jump start done in the wrong order can cause sparks near a battery that gives off flammable hydrogen gas. A frozen or cracked battery can also fail violently. Work slowly, protect your eyes and hands, and keep your own warmth in mind, because standing in the wind with bare hands is a risk too. If you are on a busy road or in a storm, your safety comes before the car.

Do this now¶

1. Make sure you are in a safe place. If you are on a road or in traffic, turn on your hazard lights, move out of the traffic lane if the car will roll, and stay well away from moving vehicles. If you feel unsafe or the weather is severe, stay inside the car and call for help using your local emergency number (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom) if you are in danger, or call your roadside assistance provider if you are not. See emergency numbers for other countries.
2. Turn off everything electrical: headlights, heater fan, radio, seat heaters, and chargers. Put the car in park (or neutral with the parking brake on for a manual) and turn the key to off.
3. Look at the battery before touching anything. If the case is bulging, cracked, leaking, or frozen solid, or if you smell rotten eggs, do not jump start it. Call for roadside help instead.
4. Check the manual or the fuse box lid for the correct jump points. Some cars have a remote positive terminal and a metal grounding post away from the battery, and some batteries are in the trunk (boot).
5. Connect the cables in the correct order (explained below), start the donor car, wait a few minutes, then try the dead car. Remove the cables in the exact reverse order and keep the engine running afterward.
6. If the car will not start after two or three tries, stop. Repeated cranking in the cold can flood the engine or overheat the starter, so move on to the troubleshooting section below.

Why batteries fail in the cold¶

A lead acid car battery makes electricity through a chemical reaction, and that reaction slows as the temperature drops. The American Automobile Association (AAA) reports that a typical battery loses about a third of its strength at freezing, 0 degrees Celsius (32 degrees Fahrenheit), and around 60 percent at minus 18 degrees Celsius (0 degrees Fahrenheit). Meanwhile, cold engine oil is much thicker, so the starter has to work harder to turn the engine over. The battery has less to give just when the engine asks for more.

Age is the biggest hidden factor. Most car batteries last roughly three to five years, and a battery that was weak in summer can fail on the first hard frost. Short trips make it worse, because the alternator does not have time to refill what the starter used. Leaving lights, a dash camera, or a charger plugged in overnight can drain a weak battery even in mild weather.

Warning signs that a battery is near the end of its life include:

• The engine turns over slowly, with a sluggish "rur rur rur" sound.
• Headlights are dim at idle and brighten when you rev the engine.
• A battery or charging warning light stays on or flickers.
• A swollen battery case, corrosion that looks like white or blue crust on the terminals, or a rotten egg smell.
• The battery is older than four or five years and has never been tested.

What a frozen battery looks like¶

A fully charged battery is hard to freeze, because the acid mix inside has a very low freezing point. A discharged battery is a different matter. As the charge drops, the liquid turns closer to water, and it can freeze at temperatures only a little below 0 degrees Celsius (32 degrees Fahrenheit). When the liquid freezes it expands, which can crack the case or warp the internal plates.

If you suspect a frozen battery, look for a bulging or box shaped case, cracks, or leaking fluid. If the battery has removable caps you may be able to see ice, but do not open caps in an emergency. Treat a bulging, cracked, or leaking battery as unsafe to jump or charge. Let a professional replace it.

Before you jump start: decide if you should¶

Jump starting is a normal job, but it is not always the right one. The checklist below helps you decide in under a minute.

You should also stop and get help in these cases:

• You cannot find the battery or the jump points and the manual is not available.
• The car is an electric vehicle or a hybrid. Many have a small 12 volt battery that can be jumped through special points, but many manufacturers give specific warnings. Read the manual first. See electric vehicle charging cable stuck for related electric vehicle guidance.
• The cables or clamps are thin, cracked, or have damaged insulation.
• You are standing in deep snow, a puddle, or near live traffic that you cannot avoid.
• Either car has a manual that says not to jump start it. Some modern cars with sensitive electronics or automatic stop start systems have special rules.

Compare your options¶

A portable jump starter pack is the safest of the home options because it removes the need for a second car. Check that it is charged every few months. Cold also drains lithium packs, so keep them inside your coat or the cabin on very cold days rather than leaving them in the trunk overnight.

How to jump start a car safely¶

You need a set of jumper cables long enough to reach between the two batteries, a donor car with a healthy battery of the same voltage (12 volt for nearly all cars), and ideally gloves and eye protection. The cables should have thick copper wire and clean clamps. Park the donor car close enough for the cables to reach but not touching the dead car, which can create an unplanned electrical path.

Step by step¶

1. Turn off both cars, set the parking brakes, and take both keys out of the ignition. Turn off all lights and accessories in both cars.
2. Open both hoods (bonnets). Find the battery or the remote jump terminals. Cars with a battery under the seat or in the trunk usually have marked terminals under the hood.
3. Identify the positive terminal, marked with a plus sign and usually a red cap, and the negative terminal, marked with a minus sign. If the terminals are corroded, wipe them with a dry cloth while wearing gloves.
4. Connect one red (positive) clamp to the positive terminal of the dead battery.
5. Connect the other red clamp to the positive terminal of the donor battery.
6. Connect one black (negative) clamp to the negative terminal of the donor battery.
7. Connect the last black clamp to a bare, unpainted metal part of the dead car, away from the battery and away from moving parts or fuel lines. A bolt on the engine block or a metal bracket works. This is called grounding, and it keeps the final spark away from the battery gas.
8. Make sure the cables are clear of belts, fans, and pulleys. Start the donor car and let it run for two to five minutes, or hold the engine at a fast idle for a minute or two if the manual allows it.
9. Try to start the dead car. If it starts, leave both cars running for a few minutes. If it only clicks or cranks slowly, wait another few minutes with the donor car running and try again.
10. Once the dead car is running, remove the cables in the exact reverse order: black from the grounded metal, black from the donor battery, red from the donor battery, red from the formerly dead battery. Do not let the clamps touch each other or any metal while any end is still connected.

Why the order matters¶

The first three connections are low risk, but the last connection can make a small spark. If that spark happens at the dead battery terminal, it can ignite hydrogen gas leaking from the battery vents. Grounding on a bare metal part away from the battery means any spark happens somewhere safer. See car battery explosion, jump start polarity reversal and battery acid burn for more on what can go wrong.

flowchart TD
    A["Car will not start in the cold"] --> B["Check battery for bulge, cracks, leaks"]
    B -->|"Damaged or frozen"| C["Do not jump. Call roadside help"]
    B -->|"Looks normal"| D["Turn off all electrics in both cars"]
    D --> E["Red to dead positive, red to donor positive"]
    E --> F["Black to donor negative, black to bare metal on dead car"]
    F --> G["Run donor car for several minutes"]
    G --> H{"Does the dead car start?"}
    H -->|"Yes"| I["Remove cables in reverse order and keep engine running"]
    H -->|"No after 2 or 3 tries"| J["Stop. Check for other causes or call for help"]
    I --> K["Drive 30 minutes or have the battery tested"]

After the car starts¶

Do not turn the car off right away. The battery has been drained and needs to recharge, and a short stop at a shop or store can leave you stranded again. Drive for at least 30 minutes if you can, preferably at steady speeds rather than stop and go traffic, and keep heavy electrical loads such as the heated rear window, seat heaters, and blower on low if possible.

Have the battery and the charging system tested as soon as you can. Many auto parts stores and garages test batteries for free or for a small fee. The test tells you whether the battery can hold a charge and whether the alternator is working.

If the battery warning light stays on after the jump, the alternator may be the real fault, and the car may stop again once the battery is drained. See alternator failure, battery warning light and loss of power at night for what to do.

Signs the problem is not the battery¶

A jump start will not fix everything. The next table helps separate battery problems from other causes of a no start in the cold.

What to do if the car still will not start¶

If you have tried the jump start properly and the engine will not run, avoid cranking for more than about ten seconds at a time. Long cranking on a cold engine overheats the starter and drains whatever power the donor car is supplying. Wait a minute between tries.

Check the basics first:

• Make sure the cable clamps are biting on clean metal. A thin layer of corrosion can stop power from flowing. Wiggle the clamps slightly to improve contact.
• Check that the battery terminals on the dead car are tight. A loose terminal can cause a no start that looks like a dead battery.
• Make sure the gear selector is in park or neutral. Many cars will not start in gear.
• Check the fuel level. A near empty tank in winter invites condensation and, in extreme cold, fuel line freeze. Keep the tank at least half full in winter.
• If you smell fuel, stop cranking and do not keep trying. Raw fuel vapor near sparks is dangerous.

If those checks do not help, the problem is probably something other than power. Call roadside assistance, stay warm, and avoid wasting the donor car's battery. For general roadside troubleshooting see emergency roadside repairs and troubleshooting.

If your key fob or door is the problem¶

Sometimes a car seems dead because the key fob battery has died in the cold, or because the doors are frozen. Push button start cars often have a backup spot to hold the fob near the start button. See key fob dead battery for how to get in and start the car, and frozen car doors, locks and windows for stuck doors and locks.

Staying safe while you wait in the cold¶

If you cannot get going and help is on the way, protect yourself first. Stay inside the car if it is safe, wear all your outer layers, and cover your head. Keep your phone warm, because cold drains phone batteries quickly. If the car stays stalled in traffic, keep the hazard lights on only if the battery can spare the power, and use them in short bursts when cars approach.

Never run a car in a closed garage while trying to warm up. Carbon monoxide builds up in minutes. If you are stranded on a winter road for a long time, read stranded in a car in a winter storm before you decide how to use the engine and heater.

Prevent a dead battery next winter¶

A little preparation prevents most cold weather battery failures. Have the battery tested before the first cold snap, particularly if it is older than three years. Clean any corrosion from the terminals with a mixture of baking soda and water, rinse with a small amount of clean water, and dry. Wear gloves and eye protection, and keep the mixture away from paint.

Other habits that help:

• Park in a garage, carport, or sheltered spot when you can. Even a few degrees makes a difference.
• Take longer trips now and then so the alternator can fully recharge the battery.
• Turn off lights, heater fan, and accessories before you switch off the engine.
• Carry a charged portable jump starter and a set of heavy gauge jumper cables.
• Consider a battery maintainer (trickle charger) if the car sits for days at a time.
• If you live where the temperature stays well below freezing, ask a garage about a battery blanket or an engine block heater. In many cold regions, block heaters and plug in posts are common.
• Replace a battery that is near the end of its life before winter, not after it fails.

See winter car kit and pre-winter vehicle check for the full pre-winter routine.

Special cases¶

Manual transmission push starts¶

A manual car can sometimes be started by rolling it, but this is a last resort. You need a flat or slightly downhill, clear, private surface and at least one helper. Turn the key to on, press the clutch down, select second gear, release the brake, and have helpers push.

When the car reaches a walking or jogging pace, release the clutch quickly and the engine should catch. Do not try this on a public road, on ice, or with an automatic. A push start also damages the catalytic converter if the engine floods with unburned fuel.

Diesel engines¶

Diesel cars usually have larger batteries and glow plugs that need a few seconds of warm up. Wait for the glow plug light to go out before cranking. Cold also thickens diesel fuel, so see diesel fuel gelling and winter DEF freeze if cranking is normal but the engine will not fire.

Start stop and hybrid systems¶

Some cars with automatic stop start use a special battery type that needs a specific charging method. Some hybrids and electric vehicles use a small 12 volt battery to wake up the high voltage system, and a dead small battery means the car appears completely dead. Check the owner's manual for the jump points and any warnings, and do not guess. When in doubt, call roadside assistance.

Motorcycles and other vehicles¶

You can usually jump a motorcycle from a car battery, but do not run the car engine while connected, because the car alternator can overload a small motorcycle battery. Use the same clamp order and keep the connection short.

Calling roadside assistance¶

Roadside help is not a failure. It is the right call when the battery is damaged, the weather is severe, you are on a fast road, or two jump attempts have failed. Many drivers have roadside cover through an insurer, a motoring club, a credit card, or the car maker, so check before you pay for a private tow.

Have this information ready when you call:

• Your exact location: road name, nearest junction, kilometer or mile marker, or the coordinates shown by your phone map.
• The make, model, color, and registration (plate) of the car.
• What the car did when you tried to start it: clicking, slow cranking, silence, or lights only.
• Whether you are in a safe place, and whether anyone in the car is a child, an older adult, or has a medical need.
• Whether the car has an electric drive, a diesel engine, or an alarm that has been going off.

If you are on a highway and cannot get the car to a safe place, leave it only if you can reach a barrier or a spot well away from traffic. Many roadside organizations advise that passengers wait outside the vehicle on the far side of a barrier on high speed roads, because a stationary car can be struck. In a blizzard or with extreme cold, the balance changes, and staying in the car may be safer. Read stranded in a car in a winter storm for that decision.

While you wait¶

Keep the interior as warm as you can without running the battery down. Wear a hat, gloves, and a scarf, and put on every dry layer you have. Move your hands and feet to keep blood flowing, and sip a warm drink if you have a flask. Keep your phone inside your clothing to protect its battery, and use airplane mode or low power mode to save charge until you need to call again.

If you have a child in the car, keep the child warm and strapped in, and do not let any person fall asleep without someone watching. Shivering that will not stop, slurred speech, and confusion are signs of dangerous cold. See hypothermia and frostbite for what to look for and how to respond. A hands-on first aid course from the Red Cross, St John Ambulance, or a local provider teaches these skills in person and is well worth the time.

A simple winter battery checklist¶

Print this or save it on your phone. Tick the items before the first hard frost.

• Battery tested by a garage or parts store, and replaced if weak.
• Terminals clean, tight, and free of crust.
• Battery hold down bracket secure so the battery does not move.
• Jumper cables of good quality, or a portable jump starter charged.
• Owner's manual in the glove box with the jump points marked.
• Gloves, a small flashlight, and a headlamp in the car.
• Roadside assistance number saved in your phone and written on paper.
• Tank at least half full to reduce condensation in the fuel system.
• Short trip habit reviewed: a longer drive at least once a week.

Common mistakes to avoid¶

Most cold weather battery trouble gets worse because of small mistakes made in a hurry. Knowing them in advance helps you stay calm.

• Cranking the starter again and again. Each try pulls a large current and can drain the donor battery as well.
• Leaving the heater fan, lights, or seat heaters on during the jump. These take current that should go to the starter.
• Connecting the last black clamp to the negative post of the dead battery. This puts the spark right where gas can collect.
• Letting the clamps touch each other while one end is connected to a battery.
• Leaning over the battery while you connect clamps. Keep your face and body back, and wear eye protection if you have it.
• Removing the cables before the dead car has settled into a steady idle.
• Forgetting to fit the battery cover and caps back on afterward.
• Ignoring the problem once the car starts, then being stranded again at the next stop.

Frequently asked questions¶

Can I jump start a car in snow or rain?¶

Yes, you can jump start a car in snow or rain if you keep the clamps and cable ends dry, avoid standing in water, and follow the correct order. Brush snow off the battery area before you open the connections, keep your gloves on, and make sure the cable clamps do not rest in puddles. If conditions are severe or the battery area is soaked, wait for roadside help.

How long should I leave the donor car running before I try to start the dead car?¶

Leave the donor car running for about two to five minutes with the cables connected, longer if the dead battery is very flat or the weather is extremely cold. Holding the donor engine at a fast idle for a minute can help, if the owner's manual allows it. If the dead car still only clicks after about five minutes, check the clamp contact and try once or twice more before calling for help.

Can a jump start damage my car?¶

A correct jump start rarely causes damage, but connecting the cables the wrong way around can blow fuses or damage electronic parts in either car. Keep the red clamps on the positive terminals and the black clamps on the donor negative terminal and a bare metal ground on the dead car. Make sure the clamps never touch each other while connected, and read the owner's manual if your car has special jump points.

How long should I drive after a jump start?¶

Drive for at least 30 minutes if you can, ideally at steady speeds, so the alternator can put some charge back into the battery. A short trip may not be enough, especially in the cold. Have the battery and charging system tested soon after, because a battery that failed once in the cold is likely to fail again.

Sources checked¶

• AAA (American Automobile Association) guidance on cold weather and battery performance and on how to jump start a car safely.
• NHTSA (United States National Highway Traffic Safety Administration) winter driving and vehicle maintenance guidance.
• Transport Canada winter driving advice on preparing a vehicle for winter.
• National Highways (England) and the UK Government winter vehicle preparation advice.
• Ready.gov (United States Department of Homeland Security) vehicle winter safety guidance.
• Vehicle manufacturer manuals for jump starting, since procedures differ by model.

Related guides¶

• Winter car kit and pre-winter vehicle check
• Car battery explosion, jump start polarity reversal and battery acid burn
• Alternator failure, battery warning light and loss of power at night
• Stranded in a car in a winter storm
• Frozen car doors, locks and windows