If your car won’t start or your battery is dead and you need a jumpstart, jumper cables can draw the voltage and amperage from another car to get your vehicle running. This article explains how to jumpstart a car with jumper cables.
How to Jumpstart a Car Battery
Items Needed:
- For safety, it’s important to wear hand and eye protection
- Jumper cables
- Another vehicle that can start the car
Inspect the Terminals and Battery
Before starting, make sure the battery terminals are not loose and can’t pivot. Corrosion is a sign of a battery draw and is a potential cause of a low charge.
Check the manufacture date of the battery. Batteries usually last about 5 years depending on the charging system and how often it is used.
If the vehicle sat for an extended period of time, like days, weeks, or months, the battery will drain down, especially with corrosion. If the battery charge falls too low, the vehicle won’t start.
Test the Voltage with a Multimeter
- Connect the positive lead to the positive battery terminal
- Connect the negative lead to the negative battery terminal
- Take a reading, which should be between 12.4 and 12.6 volts
Differences in Battery Sizes: Confirm the Other Vehicle Can Start the Car
Since there are different sized engines and battery sizes, you may see a big difference between the two different batteries.
For example:
Smaller Vehicle
- Cranking amps – 650 at 32 degrees Fahrenheit
- Cold cranking amps – 525
Larger vehicle
- Cranking amps – 985 at 32 degrees Fahrenheit
- Cold crank amps – 800
It’s harder to jumpstart a larger vehicle that requires more amps with a smaller vehicle that requires less, because the battery won’t be able to put out as much cold cranking amps.
It’s easier to jumpstart a smaller vehicle with a larger vehicle that requires more amps.
How to Properly Jumpstart a Car
Steps for Jumpstarting a Dead Battery
- Connect the Red Jumper Cable to the Positive Battery Terminal on the Good Battery
Attach the red (positive) cable to the positive terminal on the good battery. Leave the black (negative) cable hanging away from any metal it could ground to.
- Connect the Red Jumper Cable to the Positive Battery Terminal on the Bad Battery
Attach the positive cable to the positive terminal on the bad battery. Leave the black (negative) cable hanging from any metal it could ground to.
- Connect the Negative Cable to the Negative Terminal on the Good Battery
Attach the negative cable to the negative terminal on the good battery.
- Connect the Negative Cable to the Negative Terminal on the Bad Battery
Connect the negative cable to the negative terminal on the bad battery, or find a ground on the engine like a structurally integral metal mount. Grounding to the engine can prevent an explosion of gases in the battery if the connection arches or sparks. It also lets you know there is an issue with the ground if the vehicle won’t start, and it creates a fused circuit to prevent damage to either vehicles’ computers. In case the battery has shifted out internally, you won’t have an issue if something explodes.
- Optional: Connect a Multimeter to the Bad Battery
You can connect a multimeter to the bad battery. With the vehicle started, you can see if the alternator is charging the battery. Once the cables are removed, if the multimeter reads around the same voltage, that shows the alternator is still working.
This means you can take the vehicle for a drive to charge up the battery. Once the destination has been reached, you can retest the battery with the multimeter.
- Start the Vehicle with the Good Battery
Start the vehicle with the good battery and let it run for a minute to give the battery a little bit of charge.
This will prevent too much of a draw that the vehicle with the good battery won’t have issues starting in the future. - Start the Vehicle with the Bad Battery
Make sure all electronics like the radio and any switches are turned off. Start the vehicle and let it run for about a minute.
Some say it’s a good idea to rev the engine on the vehicle with the good battery when jumpstarting, but the alternator is not supposed to provide a good burst of power to the bad battery—It’s supposed charge the battery once the vehicle is started.
The goal is not to charge the bad battery but to send enough amps and volts to start the vehicle, where the vehicle’s own alternator should be charging the battery. - Take a Road Test
It’s a good idea to take the vehicle for a road test after starting so the alternator can charge the battery.
What If the Car Turns Off After the Jumper Cables Are Removed?
The car should be able to run using the alternator. You should still be able to drive and possibly charge the battery if the battery is dead. For a car that turned off and didn’t crank over again after disconnecting the jumper cables after jumpstarting the car, more than likely there is an issue with the alternator and it should be tested.
If the alternator isn’t putting out enough amperage to charge the battery, you know you’ll have an issue. If the alternator is bad and you managed to reach your destination, the battery voltage will be too low at the next start up. The alternator is meant to slowly charge the battery over time.
Related Content
- The Battery or Alternator?
- How to Test a Car Battery for Health
- Car Battery Keeps Dying?
- How to Use a Digital Multimeter
Shop Parts and Tools at 1A Auto
- Battery Charging and Jump Starting
- Multimeter
- Tools & Accessories
- Diagnostic & Measuring Tools
- Battery Tester
