Key takeaways
- A fully charged 12 V LiFePO4 battery rests at about 13.6 V and an empty one at about 10.0 V.
- 13.0 V at rest means a 12 V LiFePO4 battery is about 50 percent charged.
- 24 V and 48 V batteries read 2 and 4 times the 12 V voltages at the same charge level.
- Read voltage only after the battery rests with no load and no charger connected.
A LiFePO4 voltage chart is a table that matches a lithium iron phosphate battery's resting voltage to its state of charge, the percentage of capacity left. This guide gives the chart for 12 V batteries, the matching values for 24 V, 48 V and single 3.2 V cells, the steps to read voltage accurately, why voltage is only a rough guide on LiFePO4, and the charging and cut-off voltages to know.
What voltage is a fully charged LiFePO4 battery?
A fully charged 12 V LiFePO4 battery reads about 13.6 V at rest and 14.2 to 14.6 V while charging. An empty one reads about 10.0 V. Values vary slightly by brand, so the battery maker's own table takes priority when one exists.
The voltages in this guide come from Anker SOLIX's 12 V state-of-charge table and Battle Born's charging specifications.
12V LiFePO4 voltage chart
A 12 V LiFePO4 battery falls from 13.6 V at full charge to 10.0 V when empty, with most of its capacity between 13.3 V and 12.8 V. The chart lists resting voltage, measured with no load or charger connected.
| State of charge | Resting voltage (12 V) |
|---|---|
| 100% | 13.6 V |
| 90% | 13.4 V |
| 80% | 13.3 V |
| 70% | 13.2 V |
| 60% | 13.1 V |
| 50% | 13.0 V |
| 40% | 12.9 V |
| 30% | 12.8 V |
| 20% | 12.6 V |
| 10% | 12.0 V |
| 0% | 10.0 V |
24V, 48V and single-cell LiFePO4 voltage chart
A 24 V or 48 V LiFePO4 battery reads 2 or 4 times the 12 V voltage at the same state of charge. The reason is construction: a 12 V battery has 4 cells in series, a 24 V battery 8 and a 48 V battery 16, and a single cell carries a quarter of the 12 V value.
| State of charge | 3.2 V cell | 12 V | 24 V | 48 V |
|---|---|---|---|---|
| 100% | 3.40 V | 13.6 V | 27.2 V | 54.4 V |
| 90% | 3.35 V | 13.4 V | 26.8 V | 53.6 V |
| 80% | 3.33 V | 13.3 V | 26.6 V | 53.2 V |
| 70% | 3.30 V | 13.2 V | 26.4 V | 52.8 V |
| 60% | 3.28 V | 13.1 V | 26.2 V | 52.4 V |
| 50% | 3.25 V | 13.0 V | 26.0 V | 52.0 V |
| 40% | 3.23 V | 12.9 V | 25.8 V | 51.6 V |
| 30% | 3.20 V | 12.8 V | 25.6 V | 51.2 V |
| 20% | 3.15 V | 12.6 V | 25.2 V | 50.4 V |
| 10% | 3.00 V | 12.0 V | 24.0 V | 48.0 V |
| 0% | 2.50 V | 10.0 V | 20.0 V | 40.0 V |
How do you read LiFePO4 voltage accurately?
Read LiFePO4 voltage at rest, after disconnecting every load and charger and waiting until the reading stops changing. A reading taken during charging or under load does not match the chart.
Reading the voltage takes 3 steps:
- Switch off or disconnect all loads and chargers, including solar.
- Wait until the voltage on your meter holds steady.
- Measure across the battery terminals with a multimeter and compare the reading with the chart.
A charge controller's display often shows charging voltage, not resting voltage, so it reads high while the sun is out.
Why is voltage only a rough guide on LiFePO4?
Voltage is a rough guide because a LiFePO4 battery's voltage curve is very flat. On the 12 V chart, the drop from 80 percent to 30 percent is only 0.5 V, so a 0.1 V meter error shifts the estimate by about 10 percent.
For an exact reading, use a battery monitor with a shunt, a device that counts the amp-hours flowing in and out. Our guide to converting amp-hours to watt-hours explains the units these monitors use.
What are the charging and cut-off voltages?
A 12 V LiFePO4 battery charges at 14.2 to 14.6 V, should float below 13.6 V or not at all, and is empty at about 10.0 V. No cell should go above 3.65 V.
| Setting | 12 V | 24 V | 48 V |
|---|---|---|---|
| Charge (bulk and absorption) | 14.2 to 14.6 V | 28.4 to 29.2 V | 56.8 to 58.4 V |
| Battle Born recommended charge | 14.4 V | 28.8 V | 57.6 V |
| Float | Off, or under 13.6 V | Off, or under 27.2 V | Off, or under 54.4 V |
| Empty (0%) | 10.0 V | 20.0 V | 40.0 V |
Our guide on how to charge a LiFePO4 battery covers chargers, solar controllers and alternators, and LiFePO4 battery life explains how charging habits affect lifespan. For a ready-made LiFePO4 system with a built-in charge display, see our best portable power stations or our Redodo Power LiFePO4 battery review.
Common questions
What voltage is 50 percent for a LiFePO4 battery?
About 13.0 V for a 12 V battery, 26.0 V for a 24 V battery, 52.0 V for a 48 V battery and 3.25 V for a single cell, measured at rest.
What is the nominal voltage of a LiFePO4 battery?
3.2 V per cell. A 12 V LiFePO4 battery has 4 cells in series for 12.8 V nominal, a 24 V battery 8 cells for 25.6 V, and a 48 V battery 16 cells for 51.2 V.
Why does my LiFePO4 battery show 14 V or more?
Because it is charging or has just come off the charger. Charging voltage runs 14.2 to 14.6 V for a 12 V battery, and the reading settles to about 13.6 V once the battery rests.
Writes guides and reviews for ProductHunter.
