Want to know if your battery really lives up to its label?

To accurately measure the capacity of a small lithium-ion battery¹, use a controlled charge-discharge cycle² under standardized conditions with calibrated instruments³.

Whether you're building a DIY project⁴ or troubleshooting a power issue⁵, learning to measure capacity⁶ properly saves time and money—and prevents nasty surprises.

What does battery capacity actually mean?

Battery labels often say “3000mAh”—but what does that number really tell you?

Battery capacity refers to how much charge a battery can deliver over time, measured in milliamp-hours (mAh)⁷. Accurate testing confirms the battery’s actual performance.

Understanding battery specifications

Key specs to know:

• Nominal Voltage⁸: Usually 3.6V or 3.7V per cell
• Rated Capacity⁹: e.g., 2200mAh or 3000mAh

• Max Discharge Rate10: Given as a C-rate (e.g. 1C = full discharge in 1 hour)	Spec	Meaning
  3.7V 2600mAh 1C	Battery delivers 2600mA for 1 hour
  0.5C discharge	1300mA for 2 hours
  2C discharge	5200mA for 30 minutes (not always safe)

Always check the datasheet or label before testing. Using wrong values can shorten lifespan—or worse.

What equipment do I need?

A multimeter alone won’t cut it.

To measure capacity accurately, you need a constant current load, a charger, a voltmeter, and a timer—or a battery analyzer that combines all three.

Basic tools checklist

Tool	Function
DC Electronic Load11	Discharge battery at constant current
Digital Multimeter12	Monitor voltage during test
Charger	Charge battery fully before testing
Battery Analyzer (optional)13	Automates charge/discharge cycles

Personally, I use the ZKE Tech EBD-USB+ electronic load for small cells—it’s cheap, USB-powered, and great for repeatable tests.

How do I condition the battery before testing?

Batteries need a warm-up, just like people.

Run 2–3 full charge/discharge cycles before testing capacity to stabilize battery chemistry and remove memory effects.

Conditioning procedure:

1. Fully charge the battery¹⁴ (to 4.2V)
2. Discharge to cutoff voltage¹⁵ (usually 3.0V or 2.5V)
3. Repeat 2–3 times¹⁶

This is especially important for new, unused, or long-stored batteries.

What’s the standard test method?

Here’s the golden rule: keep it constant.

Discharge the fully charged battery at a constant current (usually 0.5C–1C), and log the current and voltage until the battery hits its cutoff voltage.

Example: 3.7V 2000mAh cell

• Charge to 4.2V
• Discharge at 1000mA (0.5C)
• Stop at 3.0V
• Time how long it runs

Formula for capacity:

[
\text{Capacity (mAh)} = \text{Current (mA)} \times \text{Time (hours)}
]

So if a 2000mAh cell runs 1 hour at 1000mA, it has a true capacity of 1000mAh. Oops!

How do I set up a controlled test?

Temperature and timing matter more than you think.

Perform the test in a room-temperature environment (20–25°C), avoid airflow changes, and use shielded leads to reduce electrical noise.

Setup tips:

• Use a fan only for equipment, not directly on the battery
• Keep charging and discharging logs
• Test each cell separately, especially in series packs

I’ve had tests go wrong just because the room temp dropped overnight—capacity readings were off by 8%.

How do I record and analyze the data?

Don’t trust your memory. Log it.

Log voltage every minute, and stop the test the moment the voltage hits the cutoff. Plot voltage vs time to visualize performance.

What to look for in results:

• Flat discharge curve: healthy cell
• Sharp voltage drop near end¹⁷: normal
• Sudden drop or dip early on: degraded cell

Use Excel, Python, or battery software (like ZKE’s PC client or BatLab) to chart and compare.

What mistakes should I avoid?

Even a small mistake can skew the test—or damage the battery.

Avoid over-discharging, testing at high current, skipping conditioning, or assuming the label is correct.

Pro tips:

• Stop discharge at 3.0V or 2.5V depending on spec
• Never discharge below 2.5V unless datasheet allows
• Use a fireproof surface during discharge
• Don’t test multiple batteries in parallel unless pre-balanced

Conclusion

Testing lithium-ion battery capacity isn’t rocket science—but it does require the right tools, method, and discipline. A good test can uncover cheap cells, bad batches, or performance loss over time.