How To Jump Start A Car: A DIYer's Guide for Battery Care & Preventative Maintenance

The sheer frustration of a dead car battery is something I know firsthand, and it turns out I'm not alone. In the past year, a staggering 35% of the over 50,000 roadside assistance calls we received were due to battery issues – that's essentially 1 in 3 times a driver was left stranded, hoping to flag down a passerby to assist and provide a donor car to jump-start their own. This eye-opening statistic left me wondering: Is it even possible to prevent this incredibly common problem? What I discovered is encouraging – yes, it is.

The following detailed guide is our attempt to do more than just explain how to jump-start a dead battery safely. We hope to teach you how to keep your battery strong from the start, or at least recognise the warning signs of a flat battery. You'll learn about battery technology, how to solve tricky problems, and useful ways to prevent issues that save you time and money.

 

Article Contents:

1. The Science Behind Jump Starting
2. Step-by-Step Jump-Starting Instructions
3. Special Considerations for Jump-Starting Modern Vehicles
4. Alternative Jump-Starting Methods
5. Advanced Troubleshooting: When Jump Starting Fails
6. DIY Battery System Diagnosis: Tools and Techniques
7. The Battery Health Checklist: For Proactive Maintenance
8. Preventing Future Battery Problems
9. Conclusion: Beyond the Jump Start

 

The Science Behind Jump Starting

Battery Technology Fundamentals

Car batteries come in several varieties, each with specific characteristics:

• Lead-acid batteries: The traditional option found in most vehicles. It contains lead plates submerged in sulfuric acid
• Absorbed Glass Mat (AGM) batteries: Features fibreglass mats that absorb the electrolyte solution. This provides better vibration resistance and power delivery 
• Enhanced Flooded Batteries (EFB): An improved version of lead-acid batteries. These batteries are for vehicles with start-stop technology 
• Lithium-ion batteries: Lighter, more expensive options used in performance and high-end vehicles

During normal operation, your battery maintains a voltage between 12.4 and 12.7v. When you start your vehicle, the voltage dips as current flows to the starter motor. A healthy battery recovers immediately. While a failing battery shows a significant voltage drop and slow recovery.

The Chemistry of Battery Discharge

Image of a Sulfated 12v Car Battery Terminal

When a battery runs out of power (is discharged), a chemical reaction occurs between the lead plates and sulfuric acid inside it. The lead plates mix with sulfuric acid, making lead sulfate and water. This reaction lowers the battery's ability to produce electricity. When you jump-start a battery, you introduce external current. This provides the necessary power to reverse the chemical reaction caused by discharge.

Step-by-Step Jump-Starting Instructions

Essential Equipment

• Jumper cables: Heavy-gauge (4-6 gauge) cables with robust clamps

• Another car (Donor): A running vehicle with a compatible battery (similar voltage)

• Optional safety gear: Gloves and eye protection are recommended

• Vehicle owner's manuals: Both for the disabled and the donor cars, in case

The Jump-Starting Process

Vehicle Preparation

Step 1: Position vehicles: Park the donor vehicle close enough to the disabled car. You want the cables to reach both batteries, but ensure the cars aren't touching.

Step 2: Secure both vehicles: Engage the parking brakes of both vehicles. Turn off all electrical components (lights, radio, climate control)

Step 3: Locate battery terminals: Identify positive (+) and negative (-) terminals on both batteries

Note: Some modern vehicles have remote jump points or covered terminals. Some modern cars locate these terminals in the boot.

Connection Sequence (Critical for Safety)

Step 4: Connect positive to disabled vehicle: Attach the red clamp to the positive (+) terminal of the dead battery.

Step 5: Connect positive to donor vehicle: Attach the other red clamp to the positive (+) terminal of the donor battery.

Step 6: Connect the negative to the donor vehicle: Attach the black clamp to the negative (-) terminal of the donor battery.

Step 7: Connect the negative to a ground point: Attach the remaining black clamp to a bare metal surface on the disabled vehicle's engine block. NB: Do not connect it to the negative terminal of the dead battery.

Starting Procedure

Step 8: Start donor vehicle: Allow it to run for 2-3 minutes to provide an initial charge.

Step 9: Attempt to start disabled vehicle: Try starting the car with the dead battery.

Step 10: If unsuccessful: Allow extra charging time (5-10 minutes) before attempting again.

Step 11: Once started: Keep both vehicles running for 15-30 minutes. This will allow the disabled vehicle's alternator to recharge the weak battery.

Disconnection Sequence (Reverse Order)

Step 12: Remove negative ground connection: Ideally, from an unpainted metal surface of the disabled vehicle.

Step 13: Remove the negative from the donor: From the negative terminal of the donor battery.

Step 14: Remove the positive terminal from the donor: From the positive terminal of the donor battery.

Step 15: Remove the positive from the previously disabled vehicle: The positive (red) terminal of the previously dead battery.

Special Considerations for Jump-Starting Modern Vehicles

Start-Stop Technology

Vehicles equipped with automatic start-stop systems typically utilise AGM (Absorbent Glass Mat) or EFB (Enhanced Flooded Batteries) batteries, which are designed for frequent cycling. These require special attention:

• Higher voltage sensitivity: Follow manufacturer guidelines precisely.

• Computer reset procedures: Some vehicles require a system reset after the battery is disconnected.

• Recovery time: Allow more extended charging periods after jump-starting.

Hybrid Vehicles

• Auxiliary batteries: Most hybrids have a separate 12v battery used for electronics and initial startup.

• High-voltage isolation: Never attempt to jump-start the high-voltage battery system.

• Specialised jump points: Many hybrid cars have specific connection points rather than direct battery access.

Vehicles with Advanced Electronics

• Voltage surge protection: Use surge protectors or specialised jump starters.

• Memory preservation: Consider using a memory saver device when disconnecting the battery.

• Manufacturer specifications: Always consult the owner's manual for specific instructions.

 

Alternative Jump-Starting Methods

Portable Jump Starter Packs

A portable power bank, such as the Noco Boost Plus, stores electrical energy in an internal battery. It provides temporary current to a flat battery in a pinch and does not need an external power source.

The Noco Boost Plus Portable  Battery Charger

 

Monitoring the charge level of the portable jump starter pack is crucial to maintaining its health. Be careful that it is not discharged beyond its rated level by prioritising charges between jump-starting events. For the reliable performance of your portable jump starter pack:

1. Verify compatibility: Ensure the jump starter has enough power rating for your vehicle.

2. Connect positive first: Attach the red clamp to the positive terminal.

3. Connect negative: Attach the black clamp to the negative terminal or ground point.

4. Power on the unit: Activate the jump starter pack.

5. Start vehicle: Attempt to start your vehicle within 30 seconds.

6. Disconnect: Remove cables in reverse order once the vehicle is running.

Battery Chargers

Battery chargers supply power to recharge a battery by converting either AC power (from the grid) or DC power (such as solar or a car alternator). Chargers turn AC/DC power into a suitable voltage and current to restore a battery’s charge.

The Mypole Automatic Smart Charger with Start Assist: Image Source

 

Not all battery chargers are created equal. The following types are available on the market to accommodate different needs:

• Smart chargers (with adjustable charge cycles and protection features)

• Trickle chargers (slow, continuous charging for maintenance)

• Fast chargers (rapid charging with higher current)

• Solar chargers (convert sunlight into electricity)

It is essential to follow the instructions provided by the charger manufacturer. For safe and reliable charging:

1. Connect charger: Attach the charger to the battery according to the manufacturer's instructions.

2. Set appropriate charging rate: Usually between 2-10 amps for maintenance charging.

3. Allow enough charging time: Usually, 1-3 hours for a meaningful charge.

4. Disconnect charger: Remove once charging is complete

5. Attempt starting: Try to start the vehicle as you usually would

 

Advanced Troubleshooting: When Jump Starting Fails

When your vehicle refuses to start even after a proper jump-start attempt. The issue likely extends beyond a simple flat battery. Consider these potential culprits:

Electrical System Issues

• Corroded connections: If enough corrosion accumulates, even slight corrosion can prevent current flow. Using light-grit sandpaper, gently wipe the terminal to remove debris.

• Faulty alternator: Test the voltage at the battery with the engine running; you should get a reading of 13.5 to 14.5 volts. (To perform this test, use a multimeter set to the appropriate DC voltage.)

• Parasitic drain: Something continuously drawing power even when the vehicle is off. This could be a faulty or hardwired light or fan that bypasses a switch and draws power from the battery. Here's a demonstration of how to perform a parasitic draw test that we thought you might find helpful.

• Damaged battery cells: Internal battery damage that prevents holding a charge.

Starter System Problems

• Defective starter motor: Listen for clicking sounds when turning the key. This indicates a mechanical problem with the starter, not a power issue.

• Solenoid failure: The component that engages the starter may be malfunctioning. It will likely need replacing.

• Ignition switch issues: Problems with the electrical connection from the key to the starter. In this instance, you will need to test the circuit's continuity.

Fuel System Concerns

• Clogged fuel filter: Your fuel lines, or the filter itself, may restrict fuel flow to the engine. Check if the fuel filter has a small amount of fuel inside. If it is completely empty, you should consult a professional.

• Fuel pump malfunction: A weak or failing fuel pump may not send enough fuel to the engine during startup. You may experience extended cranking or need many attempts to start the car. This is a good sign that it is not delivering adequate fuel pressure to the injectors.

• Empty fuel tank: This is a simple yet surprisingly common and often overlooked issue. Check your fuel gauge. Also, try shaking your vehicle while listening to a swishing sound near the fuel tank.

Diagnostic Approach

For a more proactive approach to faulty battery troubleshooting. Try to test yourself if comfortable, or take your vehicle in for an exploratory:

1. Battery testing: Using a multimeter to check voltage (12.4-12.7v when off, 13.5-14.5v when running).

2. Load testing: Professional testing measures battery performance under simulated starting conditions.

3. OBD-II diagnostics: Connecting a scanner to identify stored fault codes.

4. Circuit testing: Checking for voltage drops across connections in the starting circuit.

 

DIY Battery System Diagnosis: Tools and Techniques

Knowing effective techniques and using the right equipment is crucial for diagnosing battery and electrical system issues.

Later in this guide, I'll present ways to help you confidently identify and address battery problems before they become costly repairs or roadside emergencies.

Essential Diagnostic Equipment You'll Need

When working with electrical components, there are some essential tools you can not live without. The following is a list of electrical testing tools that can be purchased at most electrical equipment outlets. I have included some good YouTube videos to give you a crash course on how to use them:

• Digital multimeter: The cornerstone of electrical testing. This tool provides accurate measurements of voltage, resistance, and continuity.

• Battery load tester: Simulates starting conditions to evaluate battery performance under load. This can also be tested using a multimeter if it is a sophisticated enough version.

• Battery hydrometer: This device measures the specific gravity of electrolyte (battery fluid) in non-sealed batteries to assess individual cell health.

• Cable resistance tester: This test identifies high-resistance connections that may appear visually acceptable. Again, it can be done using a multimeter on the continuity or resistance analysis setting.

• Circuit analyser: Detects parasitic drains that discharge batteries during vehicle storage.

 

Try This 3-Test Systematic Testing Procedure For The Average Joe

 

Test #1: Battery State Assessment

This is a way to check the health and strength of your battery. It looks at how much energy it can still hold, how long it will last before recharging, and whether it’s working properly. This helps to determine whether a battery is still good or needs to be replaced.

1. Visual Inspection: Before anything else, check for physical damage, corrosion, leaks, or swelling. Also, inspect the terminals for dirt, corrosion, or loose connections.

2. Surface charge elimination (For accurate voltage readings): This step in the process ensures accurate voltage readings. It checks for excess charge that builds up on a battery’s plates, which can give a false voltage reading. This is how you eliminate surface charge:

Ensure that the battery has rested for 4–12 hours, or

1. For a car battery: Turn on the headlights (high beam) for 3–5 minutes.

2. For a deep-cycle battery: Connect a load that draws about 5% of the battery's capacity for 2–3 minutes.

3. Resting voltage measurement (State of charge check): This is a state of charge (SoC) check for checking a battery’s voltage. It is taken after it has been disconnected from any charger or load (i.e. rested) for at least 5 to 10 minutes. This ensures that surface charge or recent discharge doesn’t affect the reading. This assures a true indication of the battery’s state of charge. To test SoC, connect your multimeter to your battery terminals while all the electrical systems are switched off.
   A reading of:

1. 12.6v+ indicates full charge.

2. 12.2- 12.4v indicates approximately a 50% charge.

3. Below 12.0v indicates significant discharge.

4. Load testing (Checking performance under use): Check if a battery performs well under real-life conditions. It applies a temporary load and measures the voltage drop. This helps identify weak or failing batteries that may appear fine when idle but struggle under use. This test helps the battery stay strong enough to function properly. Doing so makes it easy to decide whether it needs reconditioning or replacement. To begin performing this test, you should:

1. Connect the load tester following the manufacturer's instructions.

2. Apply a load equivalent to half the battery's CCA (Cold Cranking Amps) rating. Pro Tip: A CCA rating indicates the number of amps a battery can produce and sustain for 30 seconds at -17.78°c (0°f) while maintaining at least 7.2 volts.

3. Maintain the load for 15 seconds while monitoring the voltage

4. Voltage should remain above 9.6v for a healthy battery in warm conditions

5. For temperature compensation, add 0.1v to the minimum acceptable voltage for every 5.6°c below 21°c.

5. Capacity Testing (For Deep-Cycle or Lithium Batteries): This test checks how much energy a battery can provide before it runs out. This helps see if the battery is still working as it should or if it’s getting weaker. By testing it under actual conditions, we can ensure its reliability. This helps avoid sudden failures and lets you know when it needs maintenance or replacement. To begin:

   1. To measure internal resistance, you can use a battery impedance tester. Alternatively, you could perform this test using a modular resistor with your digital multimeter. See this guide for tips:

   2. Higher resistance suggests ageing or sulfation in lead-acid batteries.

1. Discharge the battery at a controlled rate by running a constant load like the radio. Then, measure the actual capacity vs. the rated capacity.

2. Use a battery analyser or load tester to track how much energy it delivers before reaching its cutoff voltage.

3. Internal Resistance Test (Determining Efficiency and Ageing): This test measures the ease with which electricity flows through a battery. If the resistance is low, the battery can deliver power efficiently. If it’s high, the battery may struggle to provide enough power, which can mean it’s getting old or damaged. This test helps you identify a weak battery before it fails and ensures it works properly. To perform this test:

6. Recharge and Observe (For Long-Term performance tracking): The recharge and observe test checks if a battery charges properly and holds power as it should. This helps find problems like slow charging, overheating, or weak power, so you know if the battery is still good or needs replacing. To carry out this test:

1. Fully Recharge the Battery. Then, connect it to the right charger and let it charge completely.
   Check Charging Time. See if charging takes longer than usual, and keep a record for future tests.
   Monitor Heat & Voltage. Using your hand, carefully feel if it gets too hot or doesn’t reach the right voltage using your multimeter.
   Test Performance. Use the battery and see if it holds power as expected. Do this by testing the battery voltage between drives.
   Repeat if Needed. If it drains too fast, the battery might be weak or damaged.

7. Record & Analyse Results:

1. Compare your findings from these tests with the manufacturer's specifications.

2. Identify if the battery is good or needs reconditioning or replacement.

 

Test #2: Charging System Evaluation

1. Static alternator inspection: This checks an alternator’s condition while the engine is off. This test helps identify problems like loose connections, damaged wiring, or worn-out components before testing it under load.

1. Check the belt tension and condition.

2. Inspect electrical connections for corrosion or looseness.

3. Verify that the mounting bracket is fastened to stability and that there are no loose screws or bolts.

2. Dynamic charging test: This test checks how well the alternator's ability to charge the battery while the engine is running. It helps detect issues like weak charging, overcharging, or failing components. This test is crucial for making sure the vehicle’s electrical system works properly. It also ensures the battery stays charged during operation. For this test, you should:

1. Start the engine and allow it to reach normal operating temperature. This can take up to 10 minutes.

2. Using the accelerator pedal, set the engine speed to approximately 1500 RPM.

3. Measure voltage across battery terminals (13.5-14.8v indicates proper charging)

4. Activate high-draw accessories (headlights, blower motor, rear defogger)

5. With these running for a minute, test the voltage, and it should remain above 13.0v with accessories running

3. Diode ripple test: Advanced multimeters can detect excessive AC ripple. This indicates alternator diode failure and will reduce the diode's ability to charge the battery. This test ensures the alternator's rectifier diodes efficiently convert AC power to smooth DC power. Follow these steps to perform this test:

1. Prepare the vehicle by ensuring the engine is off and the battery is fully charged. Then, a digital multimeter (DMM) will be set up to measure AC voltage.

2. Start the Engine. Run the engine at idle speed. Keep all accessories (lights, radio, AC) off for an initial test.

3. Measure AC Voltage at the Battery Terminals. Place the positive (red) lead of the multimeter on the battery’s positive terminal. Place the negative (black) lead on the battery’s negative terminal. Read the AC voltage output.

4. Increase Engine Speed & Load. Slowly rev the engine to about 2000–2500 RPM. Turn on electrical accessories (such as headlights, fan, and radio) to increase the load. Observe if the AC voltage fluctuates.

5. Analyse the Readings. A healthy alternator should show an AC voltage below 0.5v. If the AC voltage is higher than 0.5v, the alternator diodes may be faulty, allowing excessive ripple.

6. Take Action Based on the Results. If the ripple voltage is too high, the alternator diodes may be failing, which leads to poor battery charging and electrical issues if you're technically able to, consider replacing the alternator or repairing the diode pack if necessary. Otherwise, this would be a good time to have your car inspected by a professional.

 

Test #3: Starting Circuit Analysis

1. Starter current draw test: This test determines whether the starter motor is working properly. Through it, we measure the current the starter draws when you turn the ignition. A high current draw could indicate problems like a faulty starter motor or a weak battery. For this test, you must:

1. Connect an inductive amp clamp/clamp meter to the battery's negative cable (not the terminal).

2. Disable the ignition system to prevent the engine from starting by turning the key completely off.

3. The normal draw for a healthy starter during cranking should range between 100 and 200 amps for smaller engines and 200 and 250 amps for larger, more powerful engines.

4. Any current draw above 250 amps indicates a faulty starter motor, which could include worn-out brushes, seized bearings (i.e. mechanical binding), or

5. If you can rule out any of these issues, your battery may be the culprit and needs to be checked.

2. Voltage drop testing: This test determines if there is any power loss in the electrical system as power flows through the vehicle. You can test this by measuring if there's too much resistance at different points. Or, in our case, we will measure it by measuring voltage drops. This will help us identify if any loose or corroded connections could cause components like the starter or lights to malfunction. To perform this test:

1. Prepare the Tools: Using a digital multimeter, set it to measure DC voltage.

2. Turn Off the Vehicle: Ensure the engine is off and all electrical systems are turned off to prevent accidents during the test.

3. Test the Voltage Across the Battery: Place the positive (red) lead on the positive terminal of the battery and the negative (black) lead on the negative terminal of the battery. Note the battery's voltage; it should be around 12.6v if fully charged.

4. Test Voltage at the Load (e.g., Starter, Lights): Turn on the system or component you’re testing (e.g., turn the key to the "start" position if testing the starter motor). Place the multimeter leads across the component, with the positive lead connected to the positive side and the negative lead connected to the negative side.

5. Measure the Voltage Drop: While the component is running, take a reading with the multimeter. Subtract the voltage reading at the component from the voltage at the battery. This gives you the voltage drop.

6. Interpret the Results: A voltage drop of more than 0.2v is usually considered too high, indicating resistance in the wiring or connections. If you notice excessive voltage drop, inspect the connections, wires, and components such as the starter for potential issues (e.g., corrosion or loose connections).

7. Repeat as Needed: Test different parts of the electrical system, such as the connection from the battery to the alternator or from the starter to the battery, to identify any other potential weak points.

 

Interpreting Test Results 

 

Fuse Removal Diagnostic Technique

This method helps identify which circuit is causing parasitic drain. Achievable by isolating specific electrical circuits and exposing underlying malfunctions or shorts. For this test:

1. Connect your ammeter or multimeter to the circuit, setting it to read the current between the negative battery terminal and the cable.

2. From your fuse box, begin removing fuses one at a time while monitoring the current draw.

3. When the current drops significantly, the last removed fuse protects the circuit, causing the drain.

4. Then, using the vehicle wiring diagrams (typically located on the fuse box cover), identify specific components in that circuit.

By methodically working through these diagnostic procedures, you can identify electrical system issues with professional-level accuracy.

This could potentially save you hundreds of pounds in diagnostic fees and prevent unexpected breakdowns.

 

The Battery Health Checklist: For Proactive Maintenance

 

Visual Inspection (Monthly)

Try to do these every month, but baking this into your routine can save you a lot of suffering when you least expect it:

• Terminal condition: Look for corrosion (white, green, or blue powder)

• Case integrity: Check for cracks, bulging, or leaking

• Cable connections: Ensure they're tight and free from damage

• Mounting security: Verify the battery is firmly secured in its tray

Performance Monitoring (Ongoing)

Watch out for these symptoms as they could present themselves at any point as you are driving around:

• Slow cranking: The engine turns over more slowly than usual.

• Dimming lights: Headlights or interior lights that fade when starting.

• Electronic glitches: Intermittent issues with vehicle electronics.

• Age consideration: Most batteries last 3-5 years; consider replacement near the end of their lifespan.

Maintenance Actions (Regularly)

• Clean terminals: Use a battery terminal brush with a baking soda solution.

• Check electrolyte levels: For non-sealed batteries, verify fluid cover plates.

• Apply terminal protectant: Use commercial spray or petroleum jelly.

• Secure connections: Ensure proper torque on terminal bolts. Refer to your vehicle's user manual or check with your local garage for more information.

 

Preventing Future Battery Problems

 

Driving Habits

• Regular long drives: Short trips don't allow full battery recharging

• Limiting accessory use: High-draw accessories strain your electrical system

• Proper shutdown: Ensure all electrical components are off before shutting down

Seasonal Considerations

• Winter precautions: Cold weather reduces battery efficiency by up to 50%

• Summer care: Extreme heat accelerates internal corrosion and water loss

• Storage preparation: Disconnect or use a maintenance charger for vehicles stored long-term

Battery Maintenance Schedule

• Monthly: Visual inspection of terminals and connections

• Quarterly: Clean terminals and check voltage

• Annually: Professional load testing and electrical system evaluation

• 3-5 years: Proactive replacement based on manufacturer recommendations

 

Conclusion: Beyond the Jump Start

Understanding car battery technology and proper jump-starting techniques is a good way to begin your journey towards mastering your vehicle's complex electrical systems.

By regularly implementing the preventative measures outlined in this guide, you can significantly reduce the likelihood of experiencing the inconvenience of a dead battery. Or, at the very least, you will know what to look for if you are stranded and help is not at hand.

Either way, it's always helpful to know you can call someone if you end up on the side of the road and can't figure out why. Sign up for a breakdown cover membership and drive with peace of mind, knowing you're not alone.

Frequently Asked Questions

Q: Can jump starting damage my vehicle's electronics?

A: When performed correctly, jump-starting is safe for modern vehicles. However, improper connections or voltage surges can damage sensitive components, so following the precise connection sequence is crucial.

Q: How long should I wait before driving after a jump start?

A: Plan to drive for at least 30 minutes at highway speeds to allow your alternator sufficient time to recharge the battery. Short drives may not fully restore battery charge.

Q: Can any vehicle jump-start my car?

A: Most petrol or diesel vehicles with 12v electrical systems can jump-start each other. However, attempting to jump-start a hybrid or electric vehicle requires special precautions and manufacturer guidelines.

Q: Is using a portable jump starter or jumper cables better?

A: Portable jump starters offer independence and eliminate the risk of electrical issues between vehicles. However, quality jumper cables remain effective when used properly and may provide more power for larger engines.