State of charge and resting voltage
| Charge | Battery | Range in the charts | Per cell |
|---|---|---|---|
| 100 % | 13.58 V | 13.57–13.60 V | 3.40 V |
| 90 % | 13.32 V | 13.24–13.40 V | 3.33 V |
| 80 % | 13.25 V | 13.22–13.35 V | 3.31 V |
| 70 % | 13.17 V | 13.13–13.30 V | 3.29 V |
| 60 % | 13.08 V | 13.08–13.25 V | 3.27 V |
| 50 % | 13.05 V | 13.04–13.20 V | 3.26 V |
| 40 % | 13.02 V | 13.00–13.13 V | 3.26 V |
| 30 % | 12.92 V | 12.88–13.07 V | 3.23 V |
| 20 % | 12.83 V | 12.80–13.00 V | 3.21 V |
| 10 % | 12.35 V | 12.00–12.71 V | 3.09 V |
Resting voltage at about 25 °C. Typical: average of the Renogy and Libre Solar tables; range: these and LiTime’s. Readings taken hours after the last charge or discharge.
What to know
From about 12.83 V to 13.32 V the voltage barely changes: on the charts that’s 20 to 90 % charge, so a reading there can’t tell 30 % from 80 %. Above about 13.38 V the battery is nearly full; below about 12.35 V it’s nearly empty. In between, only a battery monitor with a shunt shows the real charge.
Charging and limits
| Charge (absorption) | 14.00–14.40 V (maximum 14.60 V, 3.65 V per cell) |
|---|---|
| Float | 13.50 V |
| Discharge cut-off | 11.20 V (BMS) · 10.00 V absolute minimum |
| Storage | 30–40 % |
| Charging temperature | 0–60 °C for the cells, but full charging power only around 25 °C: EVE allows 3 % of it at 0 °C, 30 % at 10 °C and 80 % at 45 °C. Many batteries stop charging below 0–5 °C. |
From the datasheets and manuals in the sources: the datasheet of your battery or charger comes first.
Tips
For the real charge of a LiFePO4 battery, fit a battery monitor with a shunt: it counts the amp-hours that go in and out. Voltage is reliable only near full and near empty.
Most LiFePO4 batteries have a BMS that disconnects the load at about 2.8 V per cell (11.2 V on a 12 V battery, Victron) and stops charging in the cold: Victron batteries charge from +5 °C.
Measure at the battery terminals with everything disconnected. A meter that is off by a hundredth of a volt per cell already matters on LiFePO4 and Li-ion.
Open in the calculator →Enter the voltage you measured and get the charge with its range.
Other batteries
24 V LiFePO4 battery (8S) 48 V LiFePO4 battery (16S) LiFePO4 cell (3.2 V) 18650 / 1S LiPo cell (3.7 V) 2S Li-ion / LiPo (7.4 V) 3S Li-ion / LiPo (11.1 V) 4S Li-ion / LiPo (14.8 V) 6S LiPo (22.2 V) 36 V Li-ion battery (10S) 48 V Li-ion battery (13S) LiHV cell (4.35 V) 12 V AGM battery 12 V gel battery 12 V flooded lead-acid battery 6 V flooded lead-acid battery NiMH cell (1.2 V)
Frequently asked questions
What voltage is a 12 V LiFePO4 battery at 50 %?
About 13.05 V at rest, but on LiFePO4 that says little: from 20 to 90 % the voltage stays between about 12.83 V and 13.32 V.
What voltage is a 12 V LiFePO4 battery at 100 %?
About 13.58 V at rest, hours after charging. While charging, the charger holds it at 14.0–14.4 V.
At what voltage is a 12 V LiFePO4 battery empty?
At rest, below about 12.35 V only about 10 % is left. Under load the BMS usually cuts at 11.20 V, and the cells are rated down to 10.00 V.
Sources: the makers’ charts and datasheets listed on the calculator page.