Lithium Battery Voltage Chart: State of Charge for 12V, 24V and 48V
A lithium battery voltage chart shows roughly how full a battery is from its resting voltage. It is useful when you have only a multimeter or a basic UPS display. LiFePO4 has a very flat voltage curve, though, so voltage is a rough guide and the BMS state of charge is more accurate. The charts below give typical values; your datasheet comes first.
Updated 12 November 2026
Nominal, full and cut-off voltage
Three numbers describe a lithium battery's voltage:
- Nominal voltage: the average while discharging. 3.2V per LiFePO4 cell, 3.6 to 3.7V per NMC li-ion cell. This is the number on the label: 12.8V, 25.6V, 51.2V.
- Full charge voltage: about 3.45 to 3.65V per LiFePO4 cell while charging; 4.2V per NMC cell.
- Cut-off voltage: the lowest safe level, about 2.5 to 2.8V per LiFePO4 cell and about 3.0V per NMC cell. Inverters normally cut off well above this to protect the pack.
12V (12.8V) LiFePO4 voltage chart
Approximate resting voltage (no load, no charge for an hour):
- 100%: 13.5 to 13.6V
- 90%: about 13.4V
- 80%: about 13.3V
- 70%: about 13.2V
- 50 to 60%: about 13.1V
- 40%: about 13.0V
- 30%: about 12.9V
- 20%: about 12.8V
- 10%: about 12.5V
- 0%: about 10 to 11V (BMS near cut-off)
Notice that 20% to 90% sits within less than one volt. That is why a 12V lithium battery can look nearly full on a meter and still have only a few hours left.
24V and 48V LiFePO4 voltage chart
Multiply the 12.8V values by 2 for a 25.6V pack and by 4 for a 51.2V (16-cell) pack:
- 25.6V pack: full about 27.0 to 27.2V at rest; 50% about 26.2V; 20% about 25.6V; empty about 20 to 22V.
- 51.2V pack: full about 54.0 to 54.4V at rest; 50% about 52.4V; 20% about 51.2V; empty about 40 to 44V.
A 15-cell 48V pack is lower: multiply the per-cell values by 15 instead. This is why inverter settings must match the cell count; see lithium battery settings (Lithium Battery Settings for Growatt, Deye, Inverex and Knox).
3.7V li-ion cell voltage chart
For NMC cells found in 18650 packs, phones, e-bikes and some power stations, the curve is steeper and voltage is a better guide:
- 4.2V: 100%
- 4.0V: about 80 to 85%
- 3.85V: about 60%
- 3.7V: about 40 to 50%
- 3.6V: about 20 to 30%
- 3.4V: about 10%
- 3.0 to 3.3V: empty
A 48V (13S) e-bike pack is full at about 54.6V and near empty around 40 to 42V.
Why voltage is only a rough guide for LiFePO4
LiFePO4 holds a nearly flat voltage for most of its discharge. Load, charging current and temperature move the reading more than the actual charge does. A reading taken while the inverter is running a fan or while solar is charging can be off by 20% or more.
The BMS counts current in and out (called coulomb counting) and shows a far more accurate state of charge. Use the battery's screen, app or the inverter's lithium display where possible. See our BMS guide (Lithium Battery BMS (Battery Management System) Explained).
How to test a lithium battery with a multimeter
- Switch off the load and charger and wait at least 30 to 60 minutes.
- Set the multimeter to DC volts, red probe on positive, black on negative.
- Compare the reading with the chart above.
- For an open pack or e-bike battery, check each cell group if accessible: they should be within about 0.05V of each other.
Voltage alone cannot tell you capacity. To check real capacity, discharge from full with a known load and time it, as explained in how to check an original lithium battery (How to Check an Original Lithium Battery Before You Buy).
Using the voltage chart with your UPS or inverter
Many UPS units and basic inverters show only battery voltage, not state of charge. Use the chart this way:
- Read the voltage when the load is light and the battery is not charging, for example late at night with only a fan on.
- Expect the reading to drop a little under load and rise during charging; that is normal.
- Set the low-battery alarm a little above the cut-off so the inverter switches to grid before the BMS trips.
- If your inverter supports lithium communication, use it; the BMS state of charge is far more accurate than any voltage chart.
For UPS-specific values, see lithium battery for UPS (Lithium Battery for UPS: What Works and What to Check).
What voltage tells you a battery is bad
- The pack drops sharply under a normal load and recovers when the load is removed: high internal resistance or a weak cell.
- One cell group is much lower than the rest after a full charge: imbalance or a failing cell.
- The battery reaches full voltage very quickly and empties fast: lost capacity.
- The pack reads 0V: the BMS has cut off; see if it wakes on charge before assuming it is dead.
For branded home batteries, record the readings and contact the brand under warranty.
