Battery State of Charge Calculator

Calculate battery SOC from resting voltage or Ah consumed.

Resting voltage (no load for 1+ hour)
Reference: 25C (77F)

Voltage vs SOC Chart

Resting voltage at 25C - per 12V battery

SOC Lead Acid AGM/Gel LiFePO4
100%12.70V12.80V13.60V
90%12.50V12.60V13.40V
80%12.42V12.50V13.30V
70%12.32V12.40V13.25V
60%12.20V12.25V13.20V
50%12.06V12.10V13.15V
40%11.90V11.95V13.10V
30%11.75V11.80V13.00V
20%11.58V11.65V12.90V
10%11.31V11.40V12.00V

Important Notes

  • Voltage readings require battery to rest 1+ hour without load/charge
  • Surface charge after charging can show falsely high voltage
  • LiFePO4 has flat voltage curve - voltage is less reliable for SOC
  • Temperature affects voltage: +/-0.003V per cell per degree C
  • Lead-acid batteries should not be discharged below 50%