Your battery looks fine—until it suddenly stops working.

Lithium-ion battery failures¹ are often caused by overcharging², deep discharging, overheating, physical damage, and manufacturing defects³. These issues can reduce capacity or cause total failure.

Understanding these failure points can help you extend battery life⁴, avoid safety issues⁵, and choose more reliable products⁶ for your projects or devices.

What role do manufacturing defects play?

Ever bought a battery that dies within weeks?

Contamination, misalignment, or internal shorts from poor manufacturing are leading causes of early lithium-ion battery failure.

Common defects include:

• Metal particles inside cells⁷
• Poorly aligned electrodes⁸
• Impurities in cathode/anode materials⁹

Type of Defect	Possible Consequence
Internal short circuit	Fire, swelling, fast failure
Uneven coating	Uneven aging, reduced cycle life
Contaminated electrolyte	Increased resistance, instability

That’s why I always prefer batteries from reputable manufacturers—even for DIY builds.

How does overcharging damage batteries?

Charging should help—not hurt.

Charging above 4.2V per cell causes chemical breakdown, gas formation, and can trigger thermal runaway.

What happens during overcharge:

• Electrolyte starts to break down
• Pressure builds inside the cell¹⁰
• Lithium plating occurs on the anode¹¹
• Separator may fail, leading to internal short¹²

Cheap or fake chargers often lack voltage regulation, making overcharge one of the most common preventable causes of failure.

Why is deep discharge a problem?

Running your battery down "all the way" is tempting—but risky.

Discharging below 2.5V can cause irreversible damage to the battery’s internal structure and reduce its future capacity.

Deep discharge consequences:

• Copper dissolution from current collector¹³
• Increased internal resistance¹⁴
• Permanent loss of active lithium¹⁵

To avoid this, I always use protection boards (BMS) in my packs. It's cheap insurance.

What is thermal runaway, and how does it start?

A hot battery is more than just uncomfortable.

Thermal runaway is a chain reaction that starts with heat and ends with fire or explosion.

Triggers for thermal runaway:

• Overcharging
• External heating (e.g., near a heater)
• Internal short circuits
• Mechanical abuse

Once started, the battery gets hotter, which speeds up decomposition, creating more heat—until something burns or bursts.

How does physical damage lead to failure?

Dropped your power bank? Might want to replace it.

Punctures, dents, or even light crushing can damage the separator, leading to internal shorts.

Effects of mechanical damage:

• Separator failure
• Internal short circuit
• Swelling from gas generation
• Fire if the short ignites electrolyte

Most of my customers ask why their battery bulged after falling—this is why.

What about high temperatures?

Heat is a silent killer of battery life.

Sustained temperatures above 45°C degrade both the electrolyte and electrode structure, reducing life and stability.

What happens in heat:

• Electrolyte breaks down faster
• SEI layer becomes unstable
• Increased risk of thermal runaway

I always recommend storing batteries in a cool, shaded area—especially in summer or hot climates.

Does charging method matter?

Not all chargers are equal—and some can ruin a battery.

Fast-charging at high current or voltage damages internal layers, while unregulated charging leads to swelling or shorts.

Best practices:

• Charge at 0.5C to 1C unless datasheet says otherwise¹⁶
• Never use a charger not matched to cell voltage
• Stop charging if the cell gets hot to touch¹⁷

Using a USB boost converter without a charging chip? That’s how you fry your cell.

What is SEI degradation and why does it matter?

Every lithium-ion battery forms a protective layer—but it doesn't last forever.

The Solid Electrolyte Interphase (SEI) protects the anode, but if it grows unstable, capacity drops and failure risk rises.

Causes of SEI failure:

• High temperature
• Fast charging
• Impure electrolyte or additives

Once SEI breaks down, lithium is lost in side reactions and doesn’t come back—your battery’s effective capacity shrinks.

Can internal shorts happen naturally?

Even well-treated batteries can fail over time.

Internal shorts can occur due to dendrite formation, particle migration, or aging materials.

Watch for:

• Sudden voltage drop during use
• Abnormal heating
• Swelling or venting

This is why older batteries are less safe—even if they look fine.

Conclusion

Lithium-ion batteries fail for many reasons, but most are preventable with good charging habits, careful handling, and quality components.