LiFePO4 Voltage Chart
Approximate resting voltage values for LiFePO4 (LFP) batteries across common pack voltages. Use this chart as a quick reference for estimating state of charge from open-circuit voltage.
Why Voltage Matters
Battery voltage is the most accessible indicator of state of charge. A multimeter connected to battery terminals can reveal roughly how charged the battery is — if you know the chemistry and pack configuration. For LiFePO4 cells, the relationship between open-circuit voltage and SOC follows a well-characterized curve, though it is notably flat in the middle range.
Understanding resting voltage helps you verify BMS readings, diagnose charging issues, and estimate remaining capacity without specialized equipment. However, voltage-based SOC estimation has real limitations for LiFePO4, which is why many systems use coulomb counting as the primary method.
LiFePO4 Voltage Chart
12V nominal pack (4S) — note the flat plateau between 30–70% SOC
Values are approximate resting voltages at 25°C. Actual values vary by manufacturer.
| SOC % | 12V Pack (4S) | 24V Pack (8S) | 48V Pack (16S) | Notes |
|---|---|---|---|---|
| 100% | 13.6V | 27.2V | 54.4V | Fully charged, resting |
| 90% | 13.4V | 26.8V | 53.6V | Near top of curve |
| 80% | 13.3V | 26.6V | 53.2V | Entering flat plateau |
| 70% | 13.2V | 26.4V | 52.8V | Flat region begins |
| 60% | 13.2V | 26.4V | 52.8V | Voltage nearly constant |
| 50% | 13.1V | 26.2V | 52.4V | Midpoint of flat plateau |
| 40% | 13.1V | 26.2V | 52.4V | Voltage indistinguishable from 50–60% |
| 30% | 13.0V | 26.0V | 52.0V | Still in flat region |
| 20% | 12.9V | 25.8V | 51.6V | Beginning to drop |
| 10% | 12.6V | 25.2V | 50.4V | Steep voltage drop |
| 0% | 12.0V | 24.0V | 48.0V | Fully discharged (cutoff) |
Values are approximate. Actual voltage varies by manufacturer, cell age, temperature, and load history.
Reading the Table
The table shows open-circuit voltage (OCV) — the voltage measured after the battery has been resting with no load for at least 30 minutes. A 12V LiFePO4 pack uses 4 cells in series (4S), a 24V pack uses 8 cells (8S), and a 48V pack uses 16 cells (16S).
Notice the extremely flat voltage plateau between 30% and 70% SOC. In this range, voltage differs by only 0.1–0.2V across the entire pack. This is the defining characteristic of LiFePO4 chemistry and makes voltage-based SOC estimation unreliable in the middle range. The voltage only becomes a useful SOC indicator near the top (above 80%) and bottom (below 20%) of the charge curve.
Accuracy Notes
Manufacturer Variation
Different LiFePO4 cell manufacturers produce cells with slightly different OCV curves. A Grade A cell from one manufacturer may rest 0.02–0.05V differently from another. Always cross-reference with your specific manufacturer's datasheet.
Temperature Effects
Cold temperatures reduce open-circuit voltage. At 0°C, expect readings 0.05–0.1V lower per cell than at 25°C. Temperature compensation in the BMS or a temperature-corrected lookup table improves accuracy.
Resting Requirement
Surface charge from recent charging inflates voltage readings. For accurate OCV measurement, the battery must rest for at least 30 minutes after charge or discharge. Some manufacturers recommend 2–4 hours for best accuracy.
BMS Calibration
Many BMS units use voltage-based SOC estimation combined with coulomb counting. If the BMS SOC reading disagrees with the voltage reading, it may need recalibration. Perform a full charge-discharge-charge cycle to reset.
Practical Tips
Use voltage readings to confirm the battery is within a reasonable SOC range. For example, if your 12V LiFePO4 pack reads 12.8V after resting, you can estimate approximately 20–25% SOC. If it reads 13.4V, the battery is near full.
For applications requiring accurate SOC (such as solar storage or RV boondocking), combine voltage monitoring with a coulomb-counting BMS. Voltage alone is insufficient for precise SOC determination in the flat plateau region.
When comparing voltage readings, always measure after the battery has been idle. Load conditions change voltage significantly. A 100Ah LiFePO4 battery under 50A load will show lower voltage than the same battery at rest, even at the same SOC.
Common Mistakes
Measuring Under Load
Voltage under load is always lower than resting voltage due to internal resistance (V = OCV − I × R). Measuring while discharging gives a falsely low SOC estimate. Always disconnect the load and wait before measuring.
Ignoring Temperature
A cold battery reads lower than the chart values. Applying room-temperature voltage tables to a battery stored in a cold garage leads to underestimating SOC. Use temperature-corrected values in cold environments.
Trusting SOC from Voltage Alone
The flat plateau between 30% and 70% SOC means voltage differences of less than 0.1V. A cheap voltmeter cannot reliably distinguish 40% from 60% SOC on a 12V LiFePO4 pack. Rely on coulomb counting for the middle range.
Mixing Up Pack and Cell Voltages
Always know whether you are reading cell voltage (3.0–3.65V) or pack voltage (12–54V). Confusing the two leads to completely wrong SOC estimates. The chart values are for nominal pack voltages, not individual cells.
Try It
Use the SOC Estimator to interpolate state of charge from open-circuit voltage measurements for your specific LiFePO4 pack.
Open SOC EstimatorFrequently Asked Questions
What is the resting voltage of a fully charged LiFePO4 battery?
A fully charged LiFePO4 cell rests at approximately 3.35–3.40V. For a 12V nominal pack (4 cells in series), that is roughly 13.4–13.6V. A 24V pack (8 cells) rests at 26.8–27.2V, and a 48V pack (16 cells) at 53.6–54.4V.
Why is LiFePO4 voltage flat in the middle SOC range?
LiFePO4 has an extremely flat discharge plateau between roughly 20% and 90% SOC. Voltage stays near 3.2V per cell across most of this range, making voltage-based SOC estimation unreliable in the middle. This is why coulomb counting or a BMS with cell balancing is preferred.
Does temperature affect LiFePO4 resting voltage?
Yes. Cold temperatures lower the open-circuit voltage slightly and increase internal resistance, which causes voltage sag under load. At room temperature (25°C), the values in the chart are most accurate. At 0°C, expect roughly 0.05–0.1V lower per cell under load.
Can I use a multimeter to check LiFePO4 SOC?
A multimeter can give you a rough estimate, but only if the battery has been resting (no charge or discharge) for at least 30 minutes to several hours. Surface charge from recent charging inflates the reading. For accurate SOC, use a BMS with coulomb counting.