Lithium batteries are the backbone of modern solar systems. They power homes, offices, shops, and off-grid installations with high efficiency and long lifespan.
But when lithium batteries swell, it’s a serious warning sign—one that, if ignored, can lead to:

• Permanent capacity loss
• Fire hazards
• Explosion in extreme cases
• Complete battery failure
• Damage to inverter and charge controller

Once swelling starts, it cannot be reversed.
The only goal is prevention.

This guide explains what causes lithium battery swelling, how to avoid it, and the best maintenance practices to keep your battery safe.

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1. What Causes Lithium Battery Swelling?

Lithium battery swelling happens when gas builds up inside the cells due to chemical breakdown. The major causes are:

1. Overcharging

When the battery is charged above its safe voltage level, internal decomposition occurs, forming gas.

2. Over-discharging

Allowing lithium batteries to drop too low (below 10–20%) stresses the cells and accelerates chemical damage.

3. High Temperature

Extreme heat causes the electrolyte to break down, producing gas that inflates the battery.

4. Wrong Charge Controller Settings

Incorrect voltage/charging parameters destroy lithium cells slowly until they swell.

5. Faulty or Low-Quality BMS (Battery Management System)

Cheap batteries with weak BMS cannot protect against overcurrent, overcharging, or overheating.

6. Paralleling Batteries With Different Voltages

Connecting batteries that do not match forces one to overwork, generating heat internally.

7. Using the Wrong Charger or Inverter

Some chargers supply incorrect voltage. Some inverters back-charge improperly if settings are wrong.

8. Physical Damage

Impact, pressure, or bending can damage internal layers, causing swelling.

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2. Signs Your Lithium Battery Is About to Swell

Before visible swelling, you may notice:

• Battery heating up excessively
• Reduced backup time
• Strange chemical smell
• Battery case becoming soft
• Inverter showing unstable voltage
• Frequent BMS shutdown
• Slow charging or sudden overcharging

If you see these signs, stop using the battery and inspect immediately.

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3. How to Prevent Lithium Battery Swelling & Damage

This is where most solar installers and users get it wrong. Below are the essential steps for preventing swelling.

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1. Use Correct Charge Controller Settings (Most Important!)

Every lithium battery has exact charging parameters that MUST be set manually:

• Boost/Bulk Voltage
• Float Voltage
• Low Voltage Cut-off
• Max charging current

Example for a typical 12V LiFePO4 battery:

• Absorb/boost: 14.4V
• Float: 13.6V
• Low cut-off: 10.5–11.0V
• Max charge current: 50A (depending on battery size)

Using wrong settings leads to chemical damage—especially overcharging, the #1 cause of swelling.

Always follow the manufacturer’s datasheet.

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2. Prevent Overcharging

To avoid overcharging:

• Use an MPPT or high-quality PWM charge controller
• Ensure correct voltage settings
• Don’t use laptop chargers, universal chargers, or car chargers on solar lithium batteries
• Avoid connecting solar directly without regulation

Overcharging is the fastest way to swell a lithium battery.

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3. Prevent Deep Discharge (Don’t Let the Battery Run Down Completely)

Lithium batteries hate being drained too low.

Keep discharge above:

• 20% SOC for longevity
• 10% minimum for safety

If you constantly run the battery to 0%, expect swelling in a few months.

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4. Control Temperature—Keep Battery Cool

Lithium batteries should operate within:

• 0°C – 45°C for charging
• -20°C – 60°C for discharging
• Below 30–35°C for best health

To maintain temperature:

✔ Install batteries in a cool, ventilated room
✔ Avoid putting them inside sealed wooden boxes
✔ Use fans or vents for airflow
✔ Keep away from direct sunlight or heat sources
✔ Avoid stacking batteries directly on each other

Heat is a silent killer of lithium cells.

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5. Use High-Quality Lithium Batteries with Strong BMS

Choose batteries that include:

• Overcharge protection
• Over-discharge protection
• Temperature sensors
• Cell balancing
• Short-circuit protection

Cheap lithium batteries swell because the BMS is weak and cannot regulate charging safely.

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6. Never Mix Old and New Batteries

If you mix:

• Different brands
• Different ages
• Different voltages
• Different Ah capacity

One battery becomes overloaded and overheats internally.

Especially when paralleled, mismatched batteries = swelling guaranteed.

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7. Balance Batteries Before Connecting in Parallel or Series

If you are connecting multiple lithium batteries:

• Charge them individually to 100%
• Ensure voltage difference is less than 0.02V
• Use identical cable lengths
• Add fuses to each battery

Unbalanced batteries cause internal resistance problems and heat buildup.

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8. Use Correct Cable Sizes

Undersized cables cause:

• Resistance
• Overheating
• Voltage drop
• Battery stress

Recommended sizes:

• 1–3 kW inverter: 25–35mm²
• 3–5 kW inverter: 35–50mm²
• 5–10 kW inverter: 50–70mm²

Heat from poor wiring can lead to swelling.

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9. Avoid Overloading the Inverter

Overloading the inverter forces batteries to discharge too fast, causing:

• Rapid heat buildup
• Voltage instability
• BMS shutdown
• Permanent damage

If your inverter is undersized, upgrade it or reduce load.

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10. Store Batteries Properly

If storing for long periods:

• Charge to 40–60%
• Store in a cool, dry place
• Recharge every 3 months
• Keep battery away from dust and moisture

Do NOT store fully charged or completely drained—it accelerates swelling.

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4. What to Do If Your Lithium Battery Starts Swelling

If you notice swelling:

STOP using the battery immediately.

Then:

1. Disconnect it from the inverter
2. Switch off charging sources
3. Do NOT press or puncture it
4. Move it away from flammable materials
5. Contact the manufacturer for replacement
6. Dispose using a certified recycling center
7. Do not charge it again, even once

Swollen batteries are dangerous and unstable.

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5. Final Recommendations

To prevent lithium battery swelling:

✔ Use correct charge controller settings

✔ Avoid heat and direct sunlight

✔ Never overcharge or deeply discharge

✔ Use only quality batteries with good BMS

✔ Don’t mix different batteries

✔ Balance battery voltage before connecting

✔ Use proper cable sizes

✔ Avoid inverter overload

✔ Store properly

Following these steps makes your lithium battery last 7–15 years without swelling or early failure.