A flat battery is one of the most common reasons cars break down, and it almost always happens at the worst moment. The good news is that jump-starting is quick and safe when you follow the right order. Here is how to do it with jumper cables, how to do it with a portable jump starter, and what to check before you touch anything.
Before you start
- Read your owner's manual. Some vehicles, including many hybrids and cars with batteries in the trunk, have dedicated jump-start terminals under the hood.
- Look at the battery. If it is cracked, leaking, bulging or smells of rotten eggs, do not jump it. Call for roadside help instead.
- Never jump a frozen battery. If the battery case looks swollen or the fluid is frozen, let it thaw or replace it.
- Protect yourself. Wear gloves and eye protection if you have them, keep sparks and flames away, and remove dangling jewelry.
- Turn everything off in both cars: ignition, lights, radio and heater.
Jump-starting with jumper cables
Park the working car close enough for the cables to reach without the two vehicles touching. Put both in park or neutral with the parking brakes on. Then connect the cables in this order:
- Red clamp to the positive (+) terminal of the flat battery.
- Other red clamp to the positive (+) terminal of the good battery.
- Black clamp to the negative (−) terminal of the good battery.
- Last black clamp to an unpainted metal surface on the engine block or chassis of the car with the flat battery, away from the battery itself.
Start the working car and let it run for a few minutes. Then try starting the car with the flat battery. If it does not start, wait a few more minutes and try again. Once it is running, remove the cables in the reverse order, keeping the clamps from touching each other.
Using a portable jump starter
A portable jump starter is a compact lithium battery pack with its own clamps. You do not need a second car, which is a big advantage on quiet roads or in a parking garage.
- Make sure the jump starter is charged and switched off.
- Connect the red clamp to the positive (+) terminal and the black clamp to an unpainted metal ground point or the negative terminal, as the manual directs.
- Switch the jump starter on and wait for its ready light.
- Start the car. Most units allow several attempts, with a short rest in between.
- Once the engine is running, switch the jump starter off and remove the black clamp, then the red one.
Many jump starters include reverse-polarity protection and double as a USB power bank or flashlight. Recharge yours every few months, because it loses charge sitting in the car, especially in cold weather.
After the jump
Keep the engine running for at least 20 to 30 minutes, ideally by driving, so the alternator can recharge the battery. If the car needs another jump soon after, the battery or charging system likely needs attention. Most auto parts stores can test both for free.
Keep a kit ready
Store jumper cables or a charged jump starter in your car alongside a flashlight, gloves and reflective warning triangles. A complete roadside emergency kit covers all of these in one bag, so you are ready the next time a battery lets you down.
