Battery swelling can be dangerous, damaging equipment and creating safety risks. This issue often starts quietly but leads to serious problems if ignored.
Battery swelling is usually caused by internal gas buildup due to overcharging, overheating, deep discharge, or manufacturing defects. Preventing it requires proper charging, storage, and battery care.
I once found a swollen lithium battery inside a customer’s solar backup unit. It looked minor at first but eventually cracked the battery case and caused power loss across the entire system.
What Is Battery Swelling?
Battery swelling happens when internal chemical reactions produce gas, causing the casing to expand.
This can occur in lithium-ion, lithium-polymer, and even sealed lead-acid batteries. Swelling is a visible sign that the battery is no longer safe or stable.
Common Causes of Battery Swelling
1. Overcharging
Overcharging is one of the most common reasons for swelling.
- The battery gets too hot.
- Excessive voltage causes breakdown of the electrolyte.
- Internal pressure increases, leading to gas formation.
Solution: Use a smart charger with overcharge protection or a BMS.
2. Deep Discharging
Fully draining a battery frequently can damage internal chemistry.
- Battery becomes unstable.
- Charge cycles are shortened.
- Swelling risk increases with repeated abuse.
Solution: Avoid letting the battery voltage drop below recommended levels.
3. High Temperatures
Heat speeds up chemical reactions inside the battery.
| Temperature | Effect on Battery |
|---|---|
| < 10°C | Slower performance |
| 25–35°C | Optimal operation |
| > 45°C | Risk of swelling, damage |
Solution: Keep the battery in shaded, well-ventilated areas.
4. Manufacturing Defects
Some swelling is caused by internal flaws.
- Uneven chemical mixtures
- Bad cell sealing
- Poor-quality separators
Solution: Buy from trusted manufacturers with strict QC processes.
5. Poor Storage Practices
Storing batteries at full charge or in hot locations causes degradation.
- Lithium batteries prefer partial charge during long-term storage.
- Swelling may happen even without use if stored improperly.
Solution: Store at 40–60% charge in cool, dry places.
How to Prevent Battery Swelling
- Use a charger with built-in protections or a smart BMS.
- Never charge unattended, especially overnight.
- Avoid deep discharge—recharge before battery hits zero.
- Install proper thermal management if the system runs hot.
- Use branded, certified batteries from reliable suppliers.
- Follow voltage and temperature guidelines set by the battery manufacturer.
Signs That a Battery Is Swelling
- Casing appears bulged or soft
- Battery doesn’t sit flat anymore
- You hear a hissing sound or feel heat
- Sudden drop in performance or capacity
If you notice any of these signs, stop using the battery immediately.
Conclusion
Swollen batteries are more than just a cosmetic issue. They are a warning of internal failure and safety risk. By using high-quality batteries, avoiding overcharging, and monitoring heat, you can prevent most causes of swelling.
SANKE lithium batteries include smart BMS protection and are tested for durability, safety, and reliability. Over 5000 charge cycles, factory-direct pricing, and minimal after-sales issues—your trusted energy partner.
