why my battery not charging

The most common cause is poor contact between the charger and the battery or voltage/connection mismatch between the charger and the battery, resulting in no normal output or being cut off by the BMS/low temperature protection.

Troubleshooting steps (in order from easiest to hardest: each step follows the pattern of “phenomenon → possible causes → solutions → precautions”)

1) Check the power supply and socket.

• Symptoms: The charger has no indicator light, no response, or occasional power outages.
• Possible causes: No power to the wall socket, poor contact of the extension cord/socket, or tripping of the residual current device/circuit breaker.
• Solutions: Replace with a known working socket or power supply; check and reset the circuit breaker/GFCI; test by directly plugging the charger into the wall.
• Precautions: Disconnect the charger before operation; avoid operation in humid environments; if you suspect a wiring problem, please have it handled by an electrician.

2) Check the charger and battery connection plugs (poor plug contact).

• Symptoms: occasional disconnection during charging, overheating, sparks at the contact points, or blackening of the connectors.
• Possible causes: loose plug, oxidation of contacts, corrosion of terminals, or poor contact.
• Solution: After powering off, unplug the plug, clean the contacts (with sandpaper or contact spray), tighten the connector, and replace the damaged plug or adapter.
• Precautions: Disconnect all power sources during cleaning; avoid short-circuiting the positive and negative terminals with metal tools; use the same specification when replacing connectors.

3) Check fuses/circuit breakers

• Symptom: The charger is completely unresponsive or trips the circuit breaker the moment it is connected.
• Possible causes: The fuse inside the vehicle or charger has blown, or the external circuit breaker has tripped.
• Solution: After turning off the power, check and replace the fuse with one of the same specifications, and reset the circuit breaker; if the fuse blows frequently, the cause of the short circuit needs to be identified.
• Precautions: Use fuses of the same specifications as the original manufacturer; identify the source of overcurrent or short circuit before frequent replacements.

4) Observe the charger indicator lights/error codes.

• Symptoms: The charger has an error indicator light or displays a fault code, or it is working but remains in a protection/standby state.
• Possible causes: The charger detected an abnormality (overtemperature, overvoltage, short circuit) or communication with the BMS was abnormal.
• Solution: Consult the charger’s instruction manual for the meaning of the corresponding code and reset it according to the steps in the manual; disconnect the power, wait a few minutes, and then reconnect it to try to restore it.
• Precautions: Do not repeatedly force the connection; if the instruction manual indicates that professional repair is required, stop using the product and contact after-sales service.

5) Measure the battery terminal voltage to ensure consistency with the overall battery pack (voltage mismatch).

• Symptoms: The charger indicates that it is incompatible with the battery or cannot charge; the battery voltage is significantly low or the voltage of individual cells is inconsistent.
• Possible causes: The charger’s rated voltage/current does not match the battery pack specifications, or individual batteries in the battery pack have failed, causing an imbalance within the pack.
• Solution: Use a multimeter to measure the total battery voltage and the voltage of each individual cell, and compare them with the manufacturer’s nominal values; if the individual cell voltages are significantly inconsistent, the damaged cells need to be balanced, repaired, or replaced; confirm that the charger output specifications are consistent with the battery requirements.
• Precautions: Pay attention to polarity during measurement; be careful when measuring each cell of the battery pack to avoid short circuits; high-voltage systems should be operated by professionals.

6) Check BMS (Battery Management System) protection.

• Symptoms: The charger is connected but does not start charging; the charger indicates “protection” or a BMS fault indicator.
• Possible causes: The BMS detects undervoltage/overvoltage/overcurrent/short circuit, abnormal temperature, or communication failure and cuts off the charging path.
• Solutions: Check the BMS indicator lights or logs; reset the BMS according to the manufacturer’s instructions (usually disconnect the bus for a few minutes and then reconnect it); repair the triggering cause (replace the faulty cell, repair the sensor or wiring).
• Precautions: Do not disassemble or modify the BMS at will; complex faults should be handled by qualified maintenance personnel.

7) Consider low-temperature protection/temperature sensor issues

• Symptoms: Charging is rejected in cold environments, the charging rate is very slow, or the BMS displays low temperature protection.
• Possible causes: The battery or charger has low temperature protection logic, the temperature sensor reading is too low or it is damaged.
• Solutions: Move the vehicle or battery to a warm environment before charging; use battery insulation measures to allow the battery to warm up; check if the temperature sensor wiring is intact.
• Precautions: Do not heat the battery directly with an open flame; allow the battery to warm up slowly to avoid sudden temperature stress.

8) Check the charger’s output and for hardware malfunctions (most difficult)

• Symptoms: The charger is working but the output voltage/current is unstable, it overheats abnormally, has an odor, or there is noise from the internal fan or no output at all.
• Possible causes: damage to the charger’s internal power module, aging of components, or mismatch between output parameters and the battery pack (e.g., the wrong voltage/current specification was selected).
• Solution: Use a multimeter/ammeter to measure the charger’s no-load and load outputs to confirm if they meet the standards; check if the charger model matches the battery pack (voltage, chemical system, charging curve); if the charger is confirmed to be faulty or incompatible, please replace it or send it for professional repair.
• Precautions: The charger contains high-voltage capacitors and may remain energized even after the power is turned off. Do not attempt to disassemble or repair it yourself unless you have the necessary professional qualifications.

When to replace the charger

• The charger detected a prolonged abnormal output voltage/current or no output at all, and the problem persisted even after ruling out issues with the wiring, plug, fuse, and BMS.
• The charger continues to overheat, smoke, or have a burnt smell under normal operating conditions, or its casing or wiring is visibly damaged.
• Repair costs are close to or exceed the price of a new charger, or the charger has been in service for many years (e.g., more than 5–8 years) and its performance has significantly declined.

Three criteria for choosing a charger: 1) Voltage and battery pack compatibility: Select a charger with a rated output voltage that matches the battery pack’s nominal voltage and supports the charging modes of the battery chemistry (e.g., lead-acid/AGM/lithium iron phosphate), and has a CC/CV or manufacturer-recommended charging curve. 2) Reasonable output current and charging rate with intelligent management: The output current meets the required charging rate (both fast recovery and without over-stressing the battery); a “smart charger” with temperature compensation, automatic charging disconnection, and communication with the BMS is preferred. 3) Safety certification and durability: The charger should have relevant safety certifications (e.g., CE/UL), protection rating (IP rating), and good heat dissipation design; choose a brand with warranty and after-sales service.