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The most common cause is poor contact between the charger and the battery/vehicle plug, or a tripped fuse/circuit breaker in the vehicle, leading to charging interruption.

Investigation steps (from easiest to hardest to check):

1) Check the indicator lights on the wall power supply and charger.

• Symptom: No indicator light is displayed when the charger is plugged in, and the charger does not start.
• Possible causes: no power in the wall socket, time-delay circuit breaker tripped, power cord loose.
• Solutions: Try a known working outlet or use other devices to confirm that the outlet has power; check and reset the circuit breaker; replace the extension cord or avoid using thin wires for extensions.
• Precautions: Disconnect the charger from the vehicle’s power supply before operation to avoid live contact; do not use damaged extension cables.

2) Check the fuses and circuit breakers inside the vehicle.

• Symptom: The charger indicator light flashes abnormally or there is no output, and there is no charging current at the vehicle end.
• Possible cause: The vehicle’s main fuse has blown or the circuit breaker has tripped.
• Solution: Check and replace the fuse with one of the same specifications according to the vehicle manual, and reset the circuit breaker.
• Precautions: When replacing a fuse, you must use the same model as the original. If the fuse blows frequently, check the cause of the short circuit before replacing it.

3) Check the contact between the charger and the vehicle plug (poor plug contact).

• Phenomenon: Unstable contact during charging, fluctuating charging current or overheating during charging.
• Possible causes: Oxidation or dirt on the plug terminals, loose contact, or bent pins.
• Solution: After power is off, clean the terminals (with contact cleaner or alcohol), straighten bent pins, and tighten or replace the damaged plug.
• Precautions: Ensure power is off during cleaning; do not rub off the conductive plating with excessive force; replace the connector if there are obvious melting marks or deformation.

4) Measure the output voltage of the battery pack and charger (voltage mismatch).

• Symptom: The charger is connected but the current is extremely low or not at all; the charger displays “error voltage” or is unstable.
• Possible causes: The charger’s output voltage does not match the battery’s nominal voltage, or the charger detects an abnormal voltage and automatically stops.
• Solution: Use a multimeter to measure the battery pack terminal voltage and the charger’s no-load output voltage to confirm that the two specifications are consistent (e.g., a 36V battery with a 36V charger); if they are incompatible, stop charging and replace with a charger of the correct specifications.
• Precautions: Pay attention to polarity during measurement; do not force a low-voltage battery to be charged with a high-voltage battery or vice versa, as this will damage the battery and BMS.

5) Check BMS protection status (BMS protection)

• Symptom: The charger displays normally when connected, but the charging current is 0 or very low, and the vehicle displays a BMS error/fail to start.
• Possible causes: The BMS detects over-discharge, abnormal cell voltage, cell imbalance, or short circuit, and actively cuts off the charging circuit to protect the battery.
• Solution: Check the instrument or BMS indicator lights/fault codes, and try the reset procedure according to the manual (e.g., power off and reconnect, short-term wake-up); if the individual unit voltage is unbalanced, it may require balancing charging or professional repair.
• Precautions: Do not attempt to bypass or short-circuit the BMS to force charging; BMS protection is usually the last line of defense against further damage. For complex faults, please contact professional repair.

6) Low temperature protection prevents charging (low temperature protection)

• Symptoms: Charging fails in cold weather, charger malfunctions, or the current is very low.
• Possible cause: The battery or BMS has low-temperature protection enabled, preventing charging at low temperatures to avoid electrochemical damage.
• Solution: Move the battery or vehicle to a warm environment to restore it to the recommended temperature range before charging; if it needs to operate in a low-temperature environment, use a charger that supports low-temperature charging and has a temperature sensor.
• Precautions: Forcing charging at low temperatures will significantly shorten battery life or cause safety hazards; do not use a heater to directly heat the battery casing.

7) Inspect wires, connectors, and vehicle wiring (for wiring/grounding faults).

• Symptoms: Intermittent power outages, localized overheating, or a burning smell during charging.
• Possible causes: cable breakage, insulation damage, poor grounding, or high contact resistance causing overheating.
• Solution: After power is off, visually inspect each section of the cable and connectors. Use a multimeter to test continuity and resistance. Replace any damaged cables or connectors.
• Precautions: Power should be disconnected immediately if a burning smell or high temperature is detected; high voltage system inspections are best performed by professionals.

8) Verify the charger’s own status (charger malfunction).

• Symptom: The above checks are all normal, but the device still cannot charge, or the charger emits abnormal noise/overheats/smokes.
• Possible causes: aging of internal components in the charger, damage to the power board, or malfunction of the control circuit.
• Solution: Replace with a known working charger of the same specifications for testing. If it charges after replacement, the original charger is confirmed to be faulty. Send it to the original charger manufacturer/professional repair shop for inspection or replacement.
• Important Notes: Internal repairs require professional skills and qualified spare parts; contact the manufacturer for support first during the warranty period.

When should you replace your charger (determining when to do so):

• The charger repeatedly malfunctioned. After checking other components, they were found to be normal, but the problem was resolved after replacing the charger.
• The charger has been used for a long time (usually more than 5–7 years) and exhibits unstable output, decreased efficiency, or frequent overheating.
• The charger exhibits obvious safety hazards: smoke, a burning smell, discoloration of the casing, or signs of short circuit.
• When manufacturer testing or after-sales recommendations suggest that repair is not feasible or the cost is close to the cost of replacement.

Three criteria for choosing a charger: 1) Voltage and current matching (specification compatibility)

• Choose a charger whose output voltage strictly matches the battery pack’s nominal voltage, and whose nominal current does not exceed the battery manufacturer’s recommended maximum charging current (or slightly lower to extend lifespan).
  2) Safety and protection functions (with BMS compatibility)
• Prioritize models with overcurrent/overvoltage/short circuit/temperature protection, communication with the vehicle’s BMS, or support for temperature sensors, and possess safety certifications such as CE/UL and a reasonable IP protection rating.
  3) Interface and after-sales support (physical compatibility and repair guarantee)
• Ensure the charger’s plug/cable is compatible with the vehicle’s interface, and choose a brand with good after-sales service and warranty policies to facilitate future maintenance and spare parts replacement.

Do you need me to create a printable checklist of the above checks, or provide more specific measurement steps and recommendations for suitable charger models based on your vehicle model/battery specifications?