Charger flashing red and green

The most common cause of a charger flashing red and green lights is abnormal contact or communication between the charger and the battery/BMS (e.g., poor plug contact or loose wiring), followed by BMS/low temperature protection triggering or voltage mismatch.

Troubleshooting (in order of easiest to hardest, 6–10 steps):

Step 1

• Symptom: The charger flashes red and green immediately after being plugged in, or the indicator light changes frequently but the charger does not charge.
• Possible causes: No power from the mains/socket or unstable voltage.
• Solution: Replace with a known working socket or use a multimeter to measure the socket voltage; confirm the socket works using other appliances.
• Precautions: Disconnect the charger power before checking the socket; do not use obviously damaged sockets or extension cords.

Step 2

• Symptoms: The indicator light changes when the cable is plugged in or unplugged, or charging starts/stops intermittently.
• Possible cause: Poor plug contact (oxidation, looseness, or bent pins at the charger end, vehicle end, or intermediate extension cable connector).
• Solution: After powering off, check and clean the charging plug and socket terminals (with a clean cloth or contact cleaner), reinsert them firmly, and replace the damaged connector if necessary.
• Precautions: Always disconnect the power before cleaning; avoid scratching the terminals with a wire brush; observe several insertions and removals after reconnection to determine stability.

Step 3

• Symptom: The indicator light is flashing and the charger is not outputting any current.
• Possible cause: The fuse/circuit breaker in the charger or vehicle has blown or tripped (the fuse has been blown).
• Solution: Check the fuses/circuit breakers of the charger and the vehicle’s main circuit; replace with fuses of the same specifications or reset the circuit breakers.
• Precautions: Use only fuses of the same specifications as the original; do not short-circuit with copper wire or replace with fuses of higher rating.

Step 4

• Symptom: After the charger is connected, the red and green lights flash alternately and an error code appears or the charger fails to charge.
• Possible cause: The charger’s output voltage/current does not match the battery pack’s nominal voltage (voltage mismatch).
• Solution: Confirm that the nominal voltage of the battery pack (e.g., 36V/48V/72V) matches the rated output voltage of the charger; if they do not match, use a matching charger or replace the battery module to match the charger.
• Precautions: Avoid using chargers with incompatible voltages; incorrect matching may damage the battery or charger.

Step 5

• Symptoms: The charger is connected but displays a fault, charging is interrupted, or it does not start under low voltage conditions.
• Possible cause: The Battery Management System (BMS) has been activated and detected overvoltage/undervoltage/short circuit/individual imbalance or communication abnormality.
• Solution: Check the vehicle’s instrument panel or BMS indicators/fault codes; clear the fault or reset the BMS as described in the vehicle manufacturer’s or BMS manual; if it is a single cell imbalance, perform equalization charging or check and repair the abnormal battery cell by cell.
• Precautions: Repeated forced resets may mask the underlying problem; record the fault codes as instructed and contact professional repair if necessary.

Step 6

• Phenomenon: The charger flashes red or green or refuses to charge in low-temperature environments.
• Possible cause: Low temperature protection triggered (the charger or BMS detects that the battery temperature is too low and activates protection to prevent damage).
• Solution: Move the vehicle to a warmer environment to allow the battery to return to a rechargeable temperature; if the charger has a temperature compensation function, confirm that the temperature sensor is working properly.
• Precautions: Do not heat the battery directly with a high-temperature source (such as an open flame or a high-powered hair dryer blowing at close range); charging at low temperatures will significantly shorten battery life or cause damage.

Step 7

• Symptoms: The charger flashes red and green, accompanied by unusual noises, odors, or overheating.
• Possible causes: Failure or aging of internal components of the charger (such as capacitors, relays, control boards).
• Solution: First, disconnect the power and allow the device to cool down. Check the casing for any burn marks or leaks. If an internal malfunction is suspected, stop using the device and send it for repair or replacement.
• Precautions: The charger contains high voltage and dangerous components. Do not disassemble if you are not a professional. Continued use of a charger with an odor or that is overheating may cause a fire hazard.

Step 8

• Phenomenon: Even after multiple checks, the battery cannot be fully charged stably; there are large differences in voltage between individual cells; and the battery life after charging is abnormally short.
• Possible causes: Degradation of individual cells in the battery pack, internal short circuit, or high internal resistance causing abnormal detection and flashing of the indicator light in the charger (battery malfunction).
• Solution: Use a cell voltage tester to measure the voltage and internal resistance of each battery cell, and replace any abnormal cells or the entire battery pack; after replacement, try the charger again.
• Precautions: When replacing battery cells/batteries, use the same brand and capacity to avoid mixing old and new batteries; dispose of batteries according to recycling regulations.

When should the charger be replaced?

• If, after ruling out problems with the plug, fuse, BMS, temperature, and the battery itself, the charger continues to flash red and green or shows signs of internal malfunction (burning smell, overheating, unstable output, or damaged internal components), the charger should be replaced.
• In addition, it is recommended to replace the charger if it has been used for a long time (generally more than 5-7 years), malfunctions frequently, or if the manufacturer has stopped production and there are no repair parts available.

Three recommended standards for choosing a charger

1. Voltage and current matching: Select a charger whose output voltage is strictly consistent with the rated voltage of the battery pack and whose output current is compatible (too large or too small will affect safety and lifespan).
2. Supports BMS communication and temperature compensation: Prioritize smart chargers with BMS communication protocols, temperature sensing, and low/high temperature protection to reduce compatibility and protection conflicts.
3. Quality and after-sales service: Choose brands with qualified certifications (such as CE/UL, etc.), good reputation and clear warranty. Spare parts and technical support should be given priority when they are available.