Battery swelling is one of the common faults of electric vehicle batteries and directly affects their service life. So why do electric vehicle batteries swell? There are ten reasons below.

1. In the past, lead-acid batteries generally used the traditional cadmium-containing formula and external curing process. Cadmium-containing lead-acid batteries resist high temperature and high current well, but pollute the environment badly. Modern lead-acid batteries strictly forbid cadmium, so prolonged charging under high temperature and high current inevitably leads to swelling.

2. In summer, a charger supplying a 48V battery usually works at about 55V, while in winter the charging voltage is generally around 61V, with temperature controllable between -22 and 55 degrees Celsius. If the charging voltage set by the charger exceeds these values, the battery is being overcharged. Overcharging causes water loss and eventually thermal runaway. Most swollen batteries are swollen because of overcharging, and the swelling is far more severe in summer than in winter.

3. Poor-quality chargers do not switch the indicator light after the battery is full and do not adjust the charging current to the battery’s current, so a large number of batteries are overcharged. After repeated overcharging, the battery swells.

4. Battery charging generally should not exceed 8 hours, but many people plug in the charger and then ignore it, often charging all night. Charger and battery staying hot for a long time not only breaks the charger easily but also swells the battery.

5. Frequent use of fast-charging stations accounts for roughly 5% of swollen batteries. Fast-charging stations use high current for a short charging time, which causes severe gassing and water loss inside the battery. Long-term use is an important reason batteries swell.

6. Mixing chargers of different models also swells batteries. Batteries of different models need different chargers and are not interchangeable, but some electric vehicle users mix them during use, charging a 48V battery with a 60V charger or a 12AH battery with a 20AH charger. The mismatched charging voltage and current make the battery swell.

7. Normally an electric vehicle battery has a safety valve that releases excess pressure. In a few batteries the safety valve is defective and cannot release pressure properly, which causes swelling and deformation.

8. If the float-charge voltage is set higher than the normal value, the temperature inside the battery rises rapidly while gas release cannot keep up, and the battery deforms and swells.

9. Even when the charger is of good quality, long-term bouncing on the vehicle may crack the solder joints of its components, causing poor contact, unstable charging current, and failure of the protection function, so the battery ends up swollen.

10. Batteries baked in the summer sun, or charging environments with too high an ambient temperature, can also deform the battery case. Depending on the battery charge level, a float charge of about 2 hours after the charger light turns green is acceptable. When the ambient temperature is high, after finishing a ride let the battery surface cool down naturally before charging, and avoid charging in a high-temperature environment.