How to Check if 18650 Battery Is Good? 5 Specific Ways

Lithium-ion 18650 batteries are extremely common these days. You can find them powering everything from laptops and electric vehicles to flashlights and power tools. But how can you test 18650 battery health to determine if the cell is still in good working condition?

There are a few methods both advanced and basic that you can use to check 18650 battery quality and performance. As a professional 18650 battery packs manufacturer, I’ll walk you through some tips and techniques to test 18650 cell voltage, capacity, internal resistance and more.

Why Testing Lithium-Ion 18650 Battery Health Matters

Before jumping into the different ways to test battery health, it’s important to understand why it matters in the first place.

As lithium-ion batteries age and go through charge/discharge cycles, their performance slowly degrades over time. Internal resistance slowly rises, capacity drops, and the battery becomes less efficient at delivering power.

Eventually, every lithium-ion battery will reach the end of its usable lifespan. At this point, it has degraded to the point where it can no longer power the application it was designed for.

Being able to evaluate the condition of 18650 cells allows you to determine whether they are still good for reuse or if it’s time to recycle and replace them.

Testing battery health helps ensure dependable performance and also safety. Heavily degraded or damaged cells can potentially be hazardous if abused or misused.

So taking the time to check battery quality using the methods below helps guarantee reliable, long-lasting, and safe performance.

How to Check if 18650 Battery Is Good?

Checking 18650 Battery Voltage

The most basic way to check lithium battery health is to measure voltage. This can tell you if the battery is completely dead or still has some life.

What You Need

• Multimeter
• 18650 battery

Testing Procedure

1. Set your multimeter to DC voltage mode.
2. Attach the black multimeter test lead to the battery’s negative terminal.
3. Connect the red test lead to the positive terminal.
4. Check the voltage reading on the multimeter display.

A quality 18650 battery when fully charged should measure between 4.2V to 4.25V.

As the battery discharges with use, voltage drops gradually. When the cell reaches 3.0 to 3.2V it is essentially fully discharged or empty.

If your 18650 battery measures significantly lower than 4.2V during testing, it could mean:

• Battery is discharged and needs to be recharged
• Battery is damaged or worn out
• There is an issue with continuity inside the cell

While voltage testing is simple and fast, it doesn’t tell you the full story about an 18650’s health by itself. Additional testing provides more helpful data.

Performing an 18650 Battery Load Test

A battery load test gives a much better picture of cell performance by simulating a real-world discharge. This allows you to monitor voltage behavior under a controlled heavy load.

Abnormal voltage response while under high load can indicate internal resistance or health issues.

What You Need

• Multimeter
• Adjustable load tester OR fixed resistor like a power resistor
• 18650 battery
• Alligator clip test leads

Load Test Procedure

1. Attach the resistor load or adjustable load tester to the 18650 cell. Follow polarity markings carefully.
2. Apply your desired test load. Start with 1-2 amps of discharge current for an average high drain 18650 battery load.
3. Monitor the battery voltage with the multimeter as it’s discharging under load. Make sure voltage doesn’t drop dangerously low.
4. Compare loaded vs unloaded voltage. A healthy 18650 battery should only experience a small voltage drop when placing a load on the cell. A high voltage drop indicates abnormally high internal resistance.

Pay attention to how the battery reacts:

• Sharp voltage drop: Internal short circuit or very high internal resistance
• Gradual voltage decrease: Normal and indicates lower internal resistance

Compare similar batteries you know are good quality. Look for cells that behave abnormally or show much larger than expected voltage drop.

Checking 18650 Battery Internal Resistance

As batteries degrade, internal resistance steadily rises. By testing an 18650 battery’s internal resistance you can get an accurate health assessment.

Using a dedicated battery internal resistance tester is the most precise approach. But you can also use a multimeter to check IR across battery terminals.

What You Need

• Multimeter OR battery internal resistance tester
• 18650 lithium-ion battery

IR Testing Procedure

1. Use specialized IR tester and follow manufacturer recommendations. OR set multimeter to resistance mode.
2. Attach multimeter/IR tester leads to the positive and negative terminals of the 18650 lithium-ion cell.
3. Note resistance measurement (labeled IR). Quality 18650s normally show <100mΩ when new.
4. Compare result to battery datasheet specs to identify cells with abnormally high IR. These cells are aged or damaged.

An 18650 with very high internal resistance will struggle when powering devices demanding high discharge currents. But they may still be usable for low power draws.

Repeatedly testing a 18650 cell’s internal resistance over time provides helpful data on the rate of electrical degradation.

Testing Actual 18650 Battery Capacity

One of the best assessments of lithium-ion battery health is taking actual capacity measurements. This test shows how much energy the cell can hold compared to its rated capacity.

Since battery capacity fades as the cell ages, comparing measured vs rated capacity percentage gives you a useful metric for identifying good quality vs degraded 18650 cells.

What You Need

• 18650 battery capacity tester OR…
• Adjustable constant current discharge load
• Multimeter

Capacity Testing Procedure

1. Fully charge battery to 4.2V before testing capacity.
2. Use a dedicated 18650 battery tester that automates discharge and capacity measurement. OR…
3. Manually: Apply constant 1A discharge load to battery. Continuously monitor voltage.
4. Stop discharge when battery reaches 3.0V. This is the fully discharged state.
5. Note discharge duration from 4.2V to 3.0V. Calculate discharged capacity in mAh.
6. Compare measured capacity to original 18650 battery specifications. Quality cells will test >80% of rated capacity.

Reputable 18650 batteries fade very gradually – only around 2-3% loss per year. Significant capacity measurements less than 70% likely means the cell has reached wearout failure.

Always properly dispose of overly degraded or damaged lithium-ion batteries to avoid safety hazards. They can potentially leak, overheat violently, or catch fire if abused.

Simple Long Term 18650 Battery Health Self Discharge Test

Lithium-ion batteries are susceptible to self-discharge over long storage durations. While small amounts of self-discharge are normal, excessive discharge can indicate internal battery cell damage.

Doing a basic self-discharge test of an 18650 battery by checking voltage loss over time provides helpful data on its health.

What You Need

• Multimeter
• 18650 battery
• Method to track test duration (watch, timer, etc)

18650 Self Discharge Testing Procedure

1. Fully charge battery to 4.2V and verify initial voltage
2. Leave battery untouched for 1-4 weeks duration
3. Measure battery voltage again after test duration
4. Compare initial vs final voltage. Quality cells maintain >90% charge for a month.

Significantly higher than normal self-discharge suggests internal shorting or high internal resistance. These factors accelerate self discharge.

A very high self discharge rate definitely means an 18650 cell is heavily degraded. It should be properly disposed of and replaced.

Tips for Reusing Salvaged 18650 Batteries

Salvaging used 18650 cells from battery packs and electronics requires carefully testing to identify good performing cells suitable for reuse.

Follow these tips when considering reusing harvested 18650 cells:

• Visually inspect all cells for damage before testing
• Perform voltage, resistance, load, and self-discharge tests
• Check capacity and only reuse cells > 70% of original rating
• Match cells with similar measured capacity
• Monitor temperatures – discard cells that heat up excessively
• Don’t attempt to reuse salvaged 18650 cells showing any signs of failure or damage

Thoroughly checking used lithium-ion 18650 batteries helps ensure you only reuse cells still in good working order. This guarantees excellent performance and safety – especially for critical applications.

Stay safe and keep an eye out for more helpful electronics tips and tutorials here on the site. Let me know if you have any battery or electrical questions in the comments section!