State of Charge

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State of Charge is a calculation meant to help estimate remaining energy in the Battery.

SoC is a porportional representation; a fraction, so it is only applicable with a known total or max.
Riders all have experienced different ranges under different temperatures, various environmental conditions etc.
So full is really a subjective term, like asking when is a ballon full? Before it pops? But if you fill it with cold air then move to a warm environment, it pops.
SoC is most easily calibrated using the battery pack's voltage at rest or near rest.
Battery Voltage

This is a rough guide to correlating at rest battery voltage to the state of charge.

There is respectable unofficial guidance that this curve varies as the pack ages over its lifetime.
These figures are determined from some selection of owners with logs, with minimal experimental controls.
Warning Warning: Your mileage may literally vary!
% SoC vs Voltage
Voltage vs % SoC
Voltage per SoC At Rest
VPack VCell SoC
115.9…116.2 4.14…4.15 100
113.9…114.24 4.07…4.08 95
112.0…112.3 4.00…4.01 90
109.76…110.8 3.92…3.96 85
108.36 3.87 80
106.96 3.82 75
105.56 3.77 70
104.16 3.72 65
103.04 3.68 60
101.92 3.64 55
101.36 3.62 50
100.80 3.60 45
99.68 3.56 40
99.12 3.54 35
98.56 3.52 30
98.00 3.5 25
97.16 3.47 20
96.60 3.45 15
96.04 3.43 10
95.76 3.42 5
95.20 3.4 0

SoC Indications per protomech
  • The mobile app appears to simply show kWh using Zero's max capacity rating, i.e. present voltage times present amp hours.
  • The voltage and amp-hours are likely to be correct, but the kWh readout is a rough guide at best.
  • The percentage reading adjusts to the estimated pack maximum over time, so if the pack ages, the reported Ah and kWh readout will decrease, but not the maximum percentage.
Variance across Battery Pack Years
The sensors measuring current and temperature for the battery pack improve over the years, impacting SoC indication.
One can find multiple complaints of going into limp-home mode at 5-15% from 2014 SR owners, for example.
2017 model year bikes appear to have an increased range of current sensor calibration quality, improving that year's estimations.
Other References
Inaccurate SoC Estimate
How OEMs calculate Battery Capacity, and why it's not totally their fault they are wrong by Brandon Nozaki Miller