The quick answer is that the positive terminal is usually marked with a plus sign or colored red, while the negative terminal carries a minus sign or is colored black. If markings are missing, verify polarity with a DC voltmeter and consult the battery’s label or manufacturer documentation.
Labels and color codes
Batteries commonly use explicit symbols, color cues, or both near each terminal. Start here to quickly identify which end is what.
- Look for a plus sign (+) or a red color near one terminal, and a minus sign (−) or black color near the other.
- Check the case or terminal caps for embossed or printed + and − markings.
- Read the battery label or datasheet for terms like P+, P−, B+, B−, or similar polarity indicators.
- If a protective cap or cover is in place, it may be color-coded or labeled to indicate the terminal’s polarity.
- Note that some packs use multiple terminals (for sensing or balancing). The main positive/negative terminals are usually labeled separately from sense terminals.
When markings are clear, you can proceed with confidence or mark the terminals yourself for future reference. If markings are absent, proceed to the next cues or consult the manufacturer.
Physical cues across common battery types
Different battery types present characteristic physical cues that help distinguish terminals without relying on labels.
- Automotive lead-acid or flooded batteries: The positive terminal often has a red cover or boot and a plus symbol; the negative terminal is typically uncoated or marked with a minus.
- Sealed lead-acid (SLA) and AGM batteries: Similar conventions apply—red usually indicates positive, black or uncolored indicates negative, with plus/minus marks near posts.
- Coin and button cells: The top surface is typically the positive terminal, while the opposite side (the can) is negative.
- Rechargeable Li-ion and NiMH cylindrical cells (e.g., 18650s): The positive terminal is the raised button on the top; the negative terminal is the flat bottom of the can.
- Battery packs with multiple cells: The main positive and negative terminals are usually larger posts, often labeled P+/P− or B+/B−; additional sense or balance leads are separate.
These cues help when labels are missing, but always confirm with documentation if you’re unsure, especially in high-energy or automotive applications.
Using a multimeter to confirm polarity
A multimeter can verify polarity when labels are unclear or when you’re wiring in new equipment. Follow these steps to establish which terminal is positive.
- Ensure the battery is disconnected from any circuit or device to avoid short circuits.
- Set the multimeter to DC voltage (V with a straight line symbol).
- Place the red probe on one terminal and the black probe on the other terminal.
- Read the display: if the meter shows a positive voltage (for example, +12.6 V), the terminal under the red probe is positive relative to the other terminal. If it shows a negative value (−12.6 V), the red probe is on the negative terminal and the other terminal is positive.
- Once you’ve identified the positive terminal, you can label it on the battery or the device wiring to prevent future mistakes.
Use caution during testing: avoid shorting terminals, and if the battery is large or potentially hazardous, consider an assistant or supervisor, especially in a workshop or automotive setting.
Safety considerations when identifying terminals
Handling batteries safely reduces the risk of sparks, burns, or chemical exposure. Keep these practices in mind while identifying terminals.
- Work in a well-ventilated area and wear eye protection and gloves as needed.
- Disconnect any equipment from the battery before inspection.
- Avoid metal jewelry or tools that could create a short between terminals.
- Do not attempt to reverse polarity or connect the battery to a circuit incorrectly.
- If you’re unsure about the terminal configuration, consult the manufacturer’s manual or a professional technician.
Correctly identifying terminals before connecting devices helps prevent damage to electronics and reduces safety risks.
Summary
To determine which terminal is which on a battery, start with clear markings or color codes on the posts. If markings aren’t visible, examine the physical design for common cues (red positive, black negative; top positive on many Li-ion cylindrical cells; main positives on packs). A DC voltmeter can confirm polarity when used carefully: a positive reading with red on a terminal means that terminal is the battery’s positive, and a negative reading indicates the opposite. Always follow safety guidelines and consult the manufacturer documentation when in doubt.