Voltage to SOC (Battery Percent)
Estimate battery state of charge from open-circuit voltage with chemistry- and temperature-aware adjustments. See %SOC plus caveats for under-load readings.
How long should the battery rest before measuring OCV?
Ideally **30–60 minutes** with both charging and loads disconnected. This lets surface charge dissipate (post-charge) and voltage bounce back (post-discharge).
Why is voltage-based SOC unreliable for LiFePO₄?
LFP has a **long, flat voltage plateau** across much of its SOC range, so small voltage changes can represent **big SOC swings** (or none). Use voltage only for rough checks; for accuracy, use a **shunt-type SOC monitor**.
Do I measure at the posts or via the BMS app?
Use a **trustworthy DMM at the terminals**. BMS app voltages can be rounded or filtered; they’re useful, but a direct terminal reading is best for calibration.
How does temperature affect the reading?
Lower temps **raise OCV** (looks fuller), higher temps **lower OCV** (looks emptier). We apply a coefficient to normalize to **25 °C**, but still recommend leaving **5–15%** uncertainty unless rested and corrected.
Can I use this under load?
Not reliably. Under load, voltage sags; right after charging, it’s elevated. Treat the result as a **ballpark** and confirm with a shunt monitor if decisions (e.g., deep-discharge cutoff) matter.