State of Health (SoH)
The headline number for how much battery you have left.
State of Health (SoH) is the ratio of a battery’s present usable capacity to its original rated capacity, expressed as a percentage. A new pack is 100%; most utility warranties guarantee ≥70% at 10 years. SoH is the single number that determines warranty standing and remaining asset value.
Definition
SoH compares current maximum capacity (measured by a capacity test or estimated from operating data) to the battery’s beginning-of-life rated capacity. It declines through calendar ageing and cycling. It is distinct from State of Charge (SoC), which is how full the battery is right now.
Formula
SoH (%) = (present usable capacity ÷ rated capacity) × 100
Typical range
New: ~100%. Warranty floor: typically ≥70% at 10 years (or ≥60% at 20). LFP reaches 4,000–6,000 full cycles to 80% SoH; NMC 2,000–3,500.
Why it matters
SoH governs the warranty: if it falls below the contracted curve, you may have a claim — or, if your dispatch caused it, a liability. It also sets the revenue capacity you can actually dispatch. Tracking SoH against the contracted curve is the foundation of every BESS analytics programme.
How NuraVolt tracks it
NuraVolt estimates SoH from operating data and periodic capacity tests, trends it against the contracted degradation curve, and projects the date it will cross the warranty threshold. A degradation rate above 2× the contracted curve over a 90-day window raises a warranty-grade alert.
Frequently asked questions
See also
A single number that normalises messy partial cycling into full-cycle equivalents.
How deep each cycle goes — and what it costs in lifetime.
Turning operating data into a defensible — or contestable — warranty position.
The fault mode when SoH declines too fast.
See this on your own plants
NuraVolt turns your SCADA and BMS data into early fault detection, degradation-aware BESS analytics, and audit-ready reporting. A fixed-scope audit shows you what we’d find on your portfolio.