When small lithium-ion batteries stop working, it’s not always obvious why. Swelling, overheating, or no charging could all mean different things.

To troubleshoot small lithium-ion batteries¹, check voltage, inspect for damage, test charge/discharge behavior², monitor temperature, and use battery management data³ if available.

If you're a product developer, repair tech, or just managing a batch of small electronics, this article will help you diagnose battery problems⁴ step by step and prevent unnecessary replacements⁵.

What are the basic signs of a battery fault?

Sometimes batteries fail quietly, and sometimes they fail dramatically.

Look for voltage drops, overheating, swelling, charging failures, or sudden capacity loss. These are early warning signs.

Common symptoms

• No charging or charges extremely slowly
• Device shuts off quickly⁶ even after full charge
• Battery gets hot⁷ during normal use
• Physical swelling⁸ or deformation
• Battery voltage < 3.0V

Symptom	Likely Cause
No charging9	Dead cell, broken protection board
Swelling10	Overcharging, internal gas buildup
Fast discharge	Capacity loss, internal damage
High heat11	Overload, short circuit

These symptoms often mean the battery is stressed, damaged, or aged beyond useful life.

How to safely inspect a battery visually?

Don’t guess—look closely. A visual inspection is the first safe step.

Check for bulges, corrosion, leaks, connector damage, or anything abnormal on the battery casing.

What to look for

• Swelling¹²: gas buildup inside due to overheating or overcharging
• Cracks or dents¹³: from drops or impact
• Leaking¹⁴: electrolyte damage or internal rupture
• Connector issues: loose pins or burnt plastic

Observation	Suggestion
Smooth casing, no marks	OK to continue testing
Slight swelling	Monitor closely, do not recharge
Severe deformation	Do not reuse—dispose safely

Always wear gloves and goggles when inspecting damaged batteries.

How to test battery voltage and current?

A multimeter is your best friend when testing batteries.

Measure open-circuit voltage to check battery charge level. Use series current test to see if the battery is delivering expected output.

Voltage test

• Set multimeter to DC mode
• Connect red probe to positive terminal, black to negative
• Read voltage:
  • 4.2V = fully charged
  • 3.7V = average level
  • < 3.0V = low or damaged

Current test (optional)

• Connect multimeter in series with load
• Check if battery delivers enough current without dropping voltage

Voltage Reading	Condition
4.2V	Fully charged
3.7V	Partially charged
<3.0V	Deep discharge or cell failure

If voltage drops under small load, the battery may have high internal resistance or cell damage.

How to test battery behavior under charging?

Charging issues are often the root of battery failure.

Observe the charging curve¹⁵—lithium-ion batteries¹⁶ follow a CC-CV pattern¹⁷: constant current until 4.2V, then constant voltage until current drops.

What to check during charging

• Is voltage rising steadily?
• Does current stop after voltage reaches 4.2V?
• Does the battery overheat?
• Is the charger compatible and outputting correct voltage/current?

Symptom	Meaning
Voltage stuck below 4V	Weak cell or bad BMS
Current doesn't taper off	Faulty charger or no CV mode
Battery heats up	High internal resistance or overcurrent

If the battery doesn’t reach 4.2V or stays hot during charge, stop immediately.

How to check temperature behavior?

Temperature tells you a lot about internal health.

Use a thermometer or thermal camera to track heat during use, rest, and charging.

Temperature guide

• Charging: should stay below 45°C
• Discharging: ideally below 50°C
• Storage: 10–25°C preferred

Condition	Temp (°C)	Action
Normal	25–40°C	Safe
Warm	40–50°C	Monitor closely
Hot	>50°C	Stop use—potential runaway

Excess heat means the battery is working too hard or has internal faults.

What can a Battery Management System (BMS) tell you?

If your battery or device has a BMS chip, use it!

The BMS stores logs of voltage, temperature, charging cycles, and errors. This data helps pinpoint what went wrong.

BMS data to review

• Charge cycle count (300–500 is typical for small cells)
• Voltage per cell in multi-cell packs
• Last temperature spike
• Current draw history

Some smart batteries output this data via USB or Bluetooth. If available, always check before declaring a battery “dead.”

When to repair, replace, or recycle?

Sometimes batteries can be rebalanced or reset. Sometimes, they’re just done.

If a battery is physically damaged, fails to hold charge, or swells—it’s time to replace or recycle it.

Final decision checklist

Condition	Recommendation
Minor voltage loss	Try full CC-CV charge cycle
Low voltage but no swelling	Slow charge under supervision
Swelling or heat	Replace immediately
Mechanical damage or leakage	Recycle properly

Never ship or reuse a known damaged lithium-ion battery—it’s not worth the risk.

Conclusion

Troubleshooting small lithium-ion batteries means understanding the basics, checking carefully, and acting safely. Always monitor voltage, watch for heat, and don’t ignore physical signs. With the right tools, you can solve most battery problems before they become serious.