State of Charge (SoC) and the SoC window
How full the battery is — and why dwelling near full ages it.
State of Charge (SoC) is how full a battery is right now, 0–100%. Beyond the live reading, the SoC window you operate in matters: persistent dwell above ~80–90% accelerates calendar ageing — dramatically so for NMC — and operating outside the OEM SoC window is a common warranty exclusion.
Definition
SoC is the present charge as a fraction of usable capacity. OEMs specify an allowed SoC window (often 10–95%). Where within that window you spend time matters: high average SoC is, for NMC, the single largest controllable degradation driver.
Formula
SoC (%) = (present charge ÷ usable capacity) × 100
Typical range
OEM SoC window: typically 10–95%. Sustained dwell above 90% accelerates NMC calendar degradation by roughly an order of magnitude; LFP is much less sensitive to SoC dwell.
Why it matters
Capping upper SoC at 90% in low-revenue hours is one of the cheapest longevity levers available, especially for NMC. Conversely, leaving an arbitrage asset parked at high SoC overnight quietly burns warranty life. SoC-window violations can also void cover.
How NuraVolt tracks it
NuraVolt monitors SoC dwell distribution against the OEM window, flags prolonged high- or low-SoC dwell as warranty-relevant, and quantifies the calendar-ageing cost of the current SoC strategy.
Frequently asked questions
See also
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