Which Battery Charger Lead Is Positive: Red or Black?

Red is positive (+) and black is negative (–) on virtually all consumer battery chargers. Attach the red clamp to the battery’s positive terminal marked “+” and the black clamp to the negative terminal marked “–,” unless the charger’s instructions specify a different method. This convention applies to most automotive, marine, powersports, and small-engine chargers.

Why the Color Coding Matters

Correct polarity prevents sparks, blown fuses, damaged electronics, and potential battery failure. While many modern “smart” chargers include reverse-polarity protection, you should still verify terminal markings and connect correctly from the start to avoid risks and ensure proper charging.

How to Connect a Battery Charger Safely

The following step-by-step process outlines the safest way to hook up a typical consumer charger to a 12 V lead-acid battery, whether the battery is installed in a vehicle or on a bench.

1. Confirm compatibility: Match charger voltage and mode to the battery (e.g., 12 V lead-acid/AGM/GEL or lithium mode for LiFePO4).
2. Power down: Turn the charger off and unplug it from AC power.
3. Identify terminals: Locate “+” (positive) and “–” (negative) marks on the battery; clean any corrosion.
4. Connect positive first: Clamp the red lead to the battery’s positive (+) terminal.
5. Connect negative:
   – If the battery is out of the vehicle, clamp the black lead to the battery’s negative (–) terminal.
   – If the battery is installed, clamp the black lead to a solid, unpainted chassis/engine ground away from the battery to reduce spark risk.
6. Set the charger: Choose the correct charging mode and current (lower amps for slow/maintenance charging; higher amps for quicker charging if the battery/charger allow).
7. Start charging: Plug the charger into AC and switch it on. Monitor indicator lights or display.
8. Finish safely: Turn the charger off and unplug it, then remove the black clamp, followed by the red clamp.

Following this sequence minimizes the chance of short circuits and sparks near battery gases and helps the charger deliver the correct profile for the battery type.

Safety and Best Practices

These tips help prevent injury, equipment damage, and battery failure during charging.

• Ventilation: Charge in a well-ventilated area; lead-acid batteries can emit hydrogen gas.
• Eye and hand protection: Wear safety glasses and gloves; acid and sparks can cause injuries.
• Check labels over colors: If cables are faded or replaced, trust the battery’s “+” and “–” markings and the charger’s labels over color alone.
• Avoid cross-polarity: Never allow red and black clamps to touch; confirm connections before powering the charger.
• Use the right mode: AGM/GEL and lithium (LiFePO4) batteries require appropriate charger settings to prevent damage.
• Inspect equipment: Don’t use swollen, cracked, or leaking batteries; replace damaged cables or clamps.
• Monitor progress: Smart chargers can stay connected to maintain charge; manual chargers should be watched to avoid overcharging.

Applying these precautions reduces risk, prolongs battery life, and ensures the charger operates as designed.

Special Cases and FAQs

What about vintage positive-ground vehicles?

Polarity at the battery posts does not change with grounding scheme: the red clamp still goes to the battery’s positive (+) post and the black to negative (–). The difference is the vehicle’s chassis is connected to the positive side. When charging on-vehicle, follow the manual—some owners connect the negative clamp directly to the battery’s negative post, others to a recommended ground point to limit spark risk.

Do smart chargers prevent damage if I connect them backward?

Many modern chargers include reverse-polarity and spark protection and simply won’t start if misconnected. However, not all chargers have these features, and relying on them is not a substitute for correct hookup.

Is color coding ever different?

In consumer DC charging, red is standardized as positive and black as negative. If a charger uses non-standard colors or the insulation is faded, confirm by reading the “+” and “–” markings on the clamps, leads, or manual, and always match to the battery’s terminal symbols.

Summary

Red is positive (+) and black is negative (–) on battery chargers. Connect red to the battery’s “+” terminal and black to the “–” terminal (or a suitable chassis ground when charging in-vehicle). Verify charger settings for your battery type, follow a safe connection order, and observe basic safety practices to protect both you and your equipment.

How to tell which wire is positive on a battery charger?

On a battery charger, the positive connection is generally the red color and the negative connection is typically black. You can identify the correct terminals on the battery by looking for the + (plus) symbol for positive and the – (minus) symbol for negative. Always ensure the charger is off before connecting the leads, and connect the red/positive lead to the positive battery terminal first, followed by the black/negative lead to the negative terminal.
 
This video demonstrates how to identify the positive and negative terminals on a car battery: 1mSpinks4IntegrityYouTube · Jul 25, 2023
How to tell which terminal is positive:

• Color: The positive clamp or lead on the battery charger is usually red, and the negative is usually black. 
• Markings: Look for a red cap or a + (plus) sign stamped onto the battery to identify the positive terminal. 
• Terminal Size: In some cases, the positive terminal is larger than the negative terminal. 

Step-by-step connection: 

1. Turn off: the battery charger.
2. Connect: the red/positive lead from the charger to the positive terminal of the battery.
3. Connect: the black/negative lead from the charger to the negative terminal of the battery.
4. Turn on: the battery charger to begin the charging process.

Do you connect red or black first on a battery charger?

When using a battery charger, you should connect the red (positive) clamp first, followed by the black (negative) clamp to the respective battery terminals. This order is to ensure a completed circuit is not formed until the final connection is made, minimizing the risk of sparks and potential explosion from hydrogen gases released by the battery.
 
Connecting the Charger:

1. Turn off: the battery charger and ensure the power cord is not plugged into a wall socket. 
2. Attach the red clamp: of the charger to the positive (+) terminal of the battery. 
3. Attach the black clamp: of the charger to the negative (-) terminal of the battery. 
4. Wiggle the clamps: to ensure a secure and stable connection. 
5. Connect the charger’s power cord: to the wall socket to begin charging. 

Why This Order Matters:

• Safety: A completed electrical circuit can create a spark at the point of the last connection. 
• Hydrogen Gas: Batteries can release flammable hydrogen gas, and connecting the negative clamp to the battery can cause a spark in the very area where the gas is most concentrated, creating an explosion risk. 
• Reduced Spark Risk: By connecting the positive (red) terminal first, you avoid creating a fully completed circuit until the final, remote connection of the negative (black) clamp. 

Disconnecting the Charger:
To disconnect safely, you should reverse the process, disconnecting the black clamp first, then the red clamp.

Is red positive on battery charger?

Yes, the red wire on a battery charger is almost always the positive (+) lead, and it should be connected to the positive terminal of the battery. This is a universal convention in electrical systems, though you should always double-check for a visible + or – symbol on the battery terminals to confirm polarity before making the connection.
 
You can watch this video to learn how to connect battery charger clamps: 53sCTEK Battery ChargersYouTube · Jan 30, 2024
How to connect the charger:

1. Identify the terminals: Look for the positive (+) and negative (-) symbols on the battery. 
2. Connect the red (positive) clamp: Attach the red clamp to the positive (+) terminal on the battery. 
3. Connect the black (negative) clamp: Attach the black clamp to the negative (-) terminal on the battery or a metal ground point away from the battery. 
4. Plug in the charger: Once both clamps are securely connected, you can plug the charger into the AC outlet to begin charging. 

Key things to remember:

• Safety first: Always ensure the charger is unplugged before connecting or disconnecting the clamps. 
• Color coding: While red for positive and black for negative is standard, if colors aren’t clear, look for the +/- symbols on the battery terminals. 
• Avoid errors: Never connect the red wire to the negative terminal, as this can damage the battery and charger. 

What is the correct way to connect a battery charger?

To hook up a battery charger, connect the red (positive) clamp to the positive battery terminal or a designated positive point in the vehicle, then connect the black (negative) clamp to a good grounding point on the engine or chassis, ensuring the grounding point is metallic and unpainted. After securing the connections, plug the charger into a power outlet and set the correct voltage, if your charger has the option.
 
This video explains the process of connecting a battery charger: 59sCTEK Battery ChargersYouTube · Jan 30, 2024
Step-by-Step Guide

1. Ensure the charger is off and unplugged: before starting any connections. 
2. Locate the battery terminals: in your vehicle. The positive terminal is usually marked with a red ” +” and the negative terminal with a black ” -“. 
3. Connect the red (positive) clamp: to the positive (+) terminal of the battery. 
4. Connect the black (negative) clamp: to a grounded metal point on the vehicle’s chassis, away from the battery, to prevent sparks that could ignite the battery. 
5. Plug the charger: into a standard electrical outlet. 
6. Set the correct voltage: on the charger, typically 12V for most cars, if your model has a selector switch. 
7. Turn on the charger: to begin the charging process. 

Important Safety Considerations

• Wear safety glasses: to protect your eyes from potential sparks. 
• Avoid connecting the negative clamp to the negative terminal: directly, especially when the battery is still in the vehicle, as this can lead to dangerous arcing or battery explosion. 
• Consult your vehicle’s manual: for specific recommended charge points or procedures for your car model. 
• Keep the connections secure: to ensure proper charging and to prevent the cables from becoming disconnected. 
• For long-term maintenance, consider installing a quick-connect or eyelet terminal to the battery for easier, more consistent charging, according to this YouTube video. 

You can watch this video to learn how to install eyelet terminal connectors for easier charging: 53sNOCOYouTube · Dec 27, 2011