To jump-start a car in cold weather, connect a working battery to the dead one with jumper cables in the right order, start the donor vehicle, then start the stalled one and keep it running for at least 20 to 30 minutes. A weak battery often fails during the first major cold snap of the season, so it pays to know the steps before you are standing in a frozen parking lot.
Cold cuts battery output while making the engine harder to turn over. Kaitlynn Furse, a manager of public relations for CAA’s south-central Ontario division, told CBC News that “even a brand new battery can lose 30 per cent of its capacity in the cold.” She said modern batteries typically last only three to five years because of temperature swings and the electrical demands of vehicle electronics.
The effect shows up in roadside calls. CAA said during one winter cold snap that its call volume in the Windsor-to-Kingston region doubled from a typical 4,000 a week, with more than half of the calls battery-related. In Manitoba, CAA reported more than 1,500 rescue calls in a single day during a February 2021 cold snap when temperatures reached -30 C, compared with a typical 300 to 400 on a winter day.
A jump-start is a low-risk job for most drivers if the battery is in good condition and the steps are followed in order. It is not safe in every case, and the section below on when to stop covers the situations where you should call roadside assistance instead. Check your owner’s manual first, because some vehicles have specific jump-start terminals or warnings about their electronics.
What you need
You need a second vehicle with a healthy battery, or a portable jump starter, and a set of jumper cables long enough to reach between the two. Heavier cables carry current better in the cold. Wear gloves and eye protection if you have them, and keep a flashlight handy if it is dark.
Step 1: Check the battery and park safely
Look at the dead battery before you connect anything. Do not jump-start a battery that is frozen, cracked, leaking or swollen. Batteries release flammable gas, so keep flames and sparks away, and never lean directly over the battery while connecting cables.
Park the donor vehicle close enough for the cables to reach, but do not let the two vehicles touch. Turn off both engines, set the parking brakes and switch off lights, the heater, the radio and other accessories in both vehicles.
Step 2: Connect the red cable to the dead battery
Clip one end of the red (positive) cable to the positive (+) terminal of the dead battery. Make sure the clamp has a firm grip on the metal and that the clamps never touch each other.
Step 3: Connect the other red clamp to the good battery
Clip the other end of the red cable to the positive (+) terminal of the working battery.
Step 4: Connect the black cable to the good battery
Clip one end of the black (negative) cable to the negative (-) terminal of the working battery.
Step 5: Ground the last black clamp
Attach the other end of the black cable to an unpainted metal surface on the stalled vehicle, such as a bolt or bracket on the engine block, away from the battery. Avoid clamping it directly to the dead battery’s negative terminal. Grounding it away from the battery keeps any spark away from the gas the battery can give off.
Step 6: Start the donor vehicle
Start the working vehicle and let it run for a few minutes. This lets the good battery and alternator feed some charge into the dead one, which matters more in the cold.
Step 7: Start the stalled vehicle
Try to start the dead vehicle. If it does not start after a short attempt, wait a couple of minutes with the donor still running and try again. Avoid cranking for long stretches, which can overheat the starter. If it still will not start after a few tries, the problem may not be the battery.
Step 8: Remove the cables in reverse order
Once the engine is running, disconnect the cables in the reverse order: the black clamp from the stalled vehicle, the black clamp from the donor, the red clamp from the donor, then the red clamp from the formerly dead battery. Do not let the clamps touch each other or any metal while they are still live.
Step 9: Keep the engine running
Keep the boosted vehicle running for at least 20 to 30 minutes, or drive it a reasonable distance, so the alternator can recharge the battery. Turning the engine off too soon often leaves you stranded again.
When to stop and call for help
Call roadside assistance or a mechanic if the battery is frozen, cracked, leaking or swollen, if the car does not start after several attempts, or if it dies again soon after a successful boost. A battery that needs repeated jumps is usually near the end of its life. Have it tested and replaced before it fails for good.
Test your battery before winter arrives, since weak ones tend to give out in the first big cold snap. Portable jump starters also lose power in extreme cold, so keep them indoors or in a warmer part of the vehicle until you need them.
In Manitoba and other very cold regions, CAA’s Christia Mariash advised plugging in a block heater when temperatures drop below -15 C. “Plug it in, pull it out and make sure you see that spark,” she said. She recommended plugging in for at least three hours before travel, not necessarily overnight, and said drivers should not run a remote starter for more than two cycles in a row.
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Sources: CBC News (CAA battery advice), Global News (CAA Manitoba), Vatrer Power (jump-start steps). Confirm the procedure in your vehicle’s owner’s manual.
