Battery Health Calculator

Capacity-based state of health metrics

State of health (SoH) is driven by measured full charge capacity versus the original design value. In service logs, many lithium packs remain above 90% during early life, then decline more rapidly after sustained high temperature exposure or frequent deep discharges. A practical maintenance flag is SoH below 80%, where runtime losses become noticeable for mobile systems and reserve margins shrink for critical loads.

Cycle aging signals and practical ranges

Cycle count captures electrochemical wear from charge–discharge throughput. Light use may accumulate fewer than 200 equivalent cycles per year, while high duty devices can exceed 500. Deeper depth of discharge increases stress; for example, operating around 60–80% depth typically yields longer life than repeated 90–100% swings. Trend cycles together with SoH to separate workload effects from measurement noise.

Temperature and charge window impacts

Average temperature is one of the strongest predictors of calendar aging. Many packs experience accelerated capacity loss when regularly above 35 C, while storage near 20–25 C is generally gentler. Charge ceiling also matters: limiting maximum charge to 80–90% can reduce time spent at high voltage, improving long-term retention. Use the calculator to compare scenarios before changing fleet policies.

Internal resistance and power delivery

Internal resistance affects voltage sag and peak power capability, not just energy. A rising resistance profile can cause brownouts under transient loads even when SoH seems acceptable. If you know a baseline resistance from commissioning tests, the resistance health metric highlights degradation earlier than capacity alone. For power tools, drones, and UPS modules, resistance trends often correlate with thermal hotspots and connector wear.

Maintenance decisions and trend logging

Use a consistent test method and sampling interval, then export results to build a time series. Replace or reassign packs that fall into poor or critical status for non-critical roles. Combine runtime estimates with measured load to validate sizing assumptions; if estimated runtime diverges, review load profiles and temperature conditions. Regular comparisons help prioritize spares and reduce unplanned downtime.

FAQs

1) What does the overall health score represent?

The score blends capacity SoH, resistance health (if baseline is provided), and estimated aging penalties. It is intended for maintenance planning and trend comparison, not as a certified laboratory grading.

2) Why is nominal voltage required for mAh inputs?

mAh is charge, not energy. Voltage is needed to estimate watt-hours for runtime calculations. If you already know watt-hours, select Wh and you can skip the voltage field.

3) How should I measure full charge capacity?

Use your device telemetry, a battery analyzer, or a controlled discharge test to a defined cutoff. Keep the method consistent across checks so the trend reflects real change, not different test conditions.

4) What is a good threshold for replacement planning?

Many teams begin planning below 80% SoH, and prioritize replacement when performance constraints appear. For safety-critical or mission-critical systems, use stricter thresholds aligned with your risk and duty cycle.

5) I do not know baseline resistance. Can I still use it?

Yes. You will still get SoH, runtime estimates, and aging indicators. Add a baseline later when you can capture a “known-good” measurement using the same instrument and test setup.

6) Why does temperature affect the result so much?

Higher temperature generally accelerates side reactions and electrolyte breakdown, increasing capacity fade and resistance. Tracking temperature alongside cycles helps explain sudden drops and supports cooling or storage improvements.