LiFePO4 Voltage Calculator
Check your battery state of charge from voltage reading
Inputs
Measure at rest (no load, no charging)
Total amp-hour rating
LiFePO4 voltage reference
| Voltage (12V) | State of Charge | Status |
|---|---|---|
| 14.6V | 100% | Fully Charged |
| 13.6V | 99% | Charged |
| 13.4V | 90% | Good |
| 13.3V | 70% | Good |
| 13.2V | 40% | OK |
| 13.0V | 30% | Low |
| 12.8V | 20% | Charge Soon |
| 12.0V | 10% | Critical |
| 10.0V | 0% | Empty |
How to use this calculator
- 01Measure your battery voltage at rest (no load, no charging)
- 02Enter the voltage reading in the calculator
- 03Enter your battery capacity in Ah
- 04View your estimated state of charge and remaining capacity
Understanding LiFePO4 voltage
LiFePO4 (lithium iron phosphate) batteries have a characteristic flat discharge curve. This means voltage stays relatively stable throughout most of the discharge cycle.
Resting voltage is most accurate when measured after the battery has been at rest for 30+ minutes with no charging or discharging.
Important: These values are for single 12V LiFePO4 cells/packs. For 24V systems, double the voltages. For 48V systems, multiply by 4.
For the complete reference — 3.2V single-cell chart, 24V/48V tables, charging stages, cycle-life vs depth-of-discharge data, and the full explanation of the flat-curve problem — see our LiFePO4 Voltage Chart deep-dive.
Frequently asked questions
Why is LiFePO4 voltage hard to read?+
LiFePO4 has a very flat discharge curve. Voltage stays around 13.2-13.3V for 70% of the discharge cycle, making it difficult to estimate SOC from voltage alone. The BMS coulomb counter is more accurate.
When should I charge my LiFePO4 battery?+
LiFePO4 batteries can be discharged to 80-90% DoD, but for maximum lifespan, consider charging when SOC drops to 20-30%. Avoid letting voltage drop below 12V.
What voltage is a full LiFePO4 battery?+
A fully charged 12V LiFePO4 battery reads 14.4-14.6V. After resting, it settles to about 13.4-13.6V. The absorption voltage during charging is typically 14.2-14.6V.
Result
40.0%
Good