The approach of warmer weather and the resumption of electric mobility activities often highlight a common problem: lithium batteries that have not been used for an extended period, such as after a vacation, may no longer charge. Faced with this situation, the first reaction is often to conclude that the battery is defective. However, before drawing this conclusion, it is important to follow a methodical approach to identify the cause of the problem and attempt to resolve it.

We’ll walk you through the possible symptoms and possible solutions for these stubborn batteries.

Before any internal manipulation, the first crucial step is to carefully examine the external condition of the battery:

• Connector: Check for corrosion, deformation or signs of overheating (melted plastic, blackened areas).
• Odor: Be alert for any suspicious odors, especially a strong smell of hot plastic or chemicals.

Safety First: If you detect an abnormal odor or signs of overheating at the connector, do not attempt to charge or open the battery. Immediately isolate it in a safe place, outdoors and away from any flammable materials, due to the potential fire hazard.

If the external inspection does not reveal any abnormalities, you can proceed to carefully open the battery case.

1. Accessing the Cells and BMS: Generally, to access the cells and the battery management system (BMS), it is necessary to remove a first protective plastic film (often blue) and an insulating sheet (often yellow) using a cutter. Be extremely careful during this step to avoid damaging the cells with the blade.
2. Voltage Measurement: Once the BMS is accessible, the first measurement to be made is the overall battery voltage. Use a multimeter to measure the voltage between the negative output pole of the BMS and the positive output pole.
3. Voltage Interpretation: If the measured voltage is significantly lower than the nominal voltage indicated on the battery, this confirms a deep discharge due to prolonged non-use.

In the case of a deep discharge, using a standard charger supplied with the device may not be enough to restart the battery. It is then recommended to use a professional charger capable of delivering a low current for a gradual reset.

1. Professional Charger Connection: Connect the positive pole of the charger to the positive input of the BMS and the negative pole of the charger to the negative input of the BMS.
2. Careful and Supervised Charging: Charging must be carried out with great caution and under constant supervision. Stay near the battery for the entire duration of the initial charge. Set the charger to a voltage corresponding to the nominal voltage of the battery.
3. Warning Signs: Be extremely vigilant for any abnormal signs during charging:
   • Suspicious smell
   • Excessive battery heating
   • Smoke emission

If any of these signs appear, immediately stop charging and isolate the battery outdoors, away from any fire hazard.

If charging is normal and the battery reaches full charge, you can proceed with reassembly:

1. Reassembly: Replace the insulating sheet and the protective plastic film.
2. Test with the Standard Charger: Then reconnect the battery to its original charger to verify that it is charging correctly.

By following these steps carefully and always prioritizing safety, you can diagnose and potentially resolve problems with unused lithium batteries.