Live Demo — Battery State of Charge Calculator
Set your battery capacity, voltage, starting SOC and low-voltage protection point, then enter load current and duration to compute the resulting SOC.
Battery State of Charge Calculator
Free professional calculator for battery state of charge (SOC) in solar street lighting systems. Enter the rated capacity, system voltage, starting SOC and low-voltage protection set-point, then define the load current and duration to estimate the remaining charge by coulomb counting, see the depth of discharge, and check how long the battery can keep supplying power above the protection red line.
Key Features
Battery Parameters
Set rated capacity in ampere-hours and choose the system voltage (12V / 24V / 48V).
Protection Set-Point
Configure the controller low-voltage protection SOC, typically 15-30%, as the discharge safety line.
Coulomb Counting
Tracks SOC from current and time via SOC = SOC_old - I × Δt / C, with positive current for discharge and negative for charge.
Discharge Conditions
Enter the load current and the operating duration to estimate the exact charge drawn from the battery.
Remaining Margin
Shows the remaining dischargeable capacity above the low-voltage protection point and the equivalent backup hours.
Voltage Reference
Built-in 12V LiFePO4 open-circuit voltage vs SOC look-up table for quick field cross-checking.
Technical Specifications
| Platform | HTML5 Web App | Android (via WebView) |
| Core Calculation | SOC = SOC_old - I × Δt / C (coulomb counting) |
| Battery Capacity | User-defined (Ah) |
| System Voltage | 12V / 24V / 48V |
| Initial SOC | 0% - 100% |
| Protection SOC | 15% - 30% typical |
| Load Current | Positive discharge / negative charge (A) |
| Duration | Sampling / discharge interval (h) |
| Efficiency | 0.95 - 0.98 charge / discharge |
| Industry Standards | IEC 61427-1, IEEE 485 |
| Output | End SOC (%), Ah consumed, remaining capacity |
Frequently Asked Questions
What is battery state of charge (SOC)?
SOC expresses the remaining battery capacity as a percentage of its rated capacity. It is the core indicator used by battery management systems to control dimming, low-voltage protection and charge management, preventing over-discharge and over-charge.
How is SOC estimated with coulomb counting?
The calculator integrates current over time: SOC(t) = SOC(t-1) - ∫(I × η / C) dt, in discrete form SOC_new = SOC_old - I × Δt / C. Discharge current is positive and lowers SOC; charge current is negative and raises it.
What is the low-voltage protection SOC?
It is the SOC set-point (typically 15-30%) at which the controller disconnects the load to protect the battery. The calculator reports the remaining dischargeable capacity above this line, so you know how much margin is left.
Can SOC be estimated from voltage alone?
Yes, using the V-SOC look-up curve, but LiFePO4 has a very flat voltage plateau in the middle SOC range, so voltage-only estimation has large errors. A hybrid of coulomb counting with voltage or full-charge calibration is recommended.
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