Path-Q Solar
How does battery degradation affect backup capacity over time?
Answer
Battery degradation reduces the usable energy available from a full charge, so the same loads run for less time as the battery ages. A sound evaluation uses the manufacturer's warranty capacity-retention terms, expected cycling and temperature, and a replacement or augmentation assumption.
Key points
- Capacity decline is different from inverter power capability and may not reduce peak power immediately.
- High temperatures, deep cycles, frequent cycling, and long periods at extreme state of charge can affect aging.
- Warranty limits may specify a minimum retained capacity or throughput conditions.
What it depends on
- Battery chemistry and design
- Operating temperature and cycling pattern
- Depth and frequency of discharge
- Warranty capacity-retention terms
- Required backup duration later in the system's life
Risks and trade-offs
- Sizing only for new-battery capacity can overstate future outage duration.
- Designing for end-of-warranty capacity may increase initial cost.
- Actual degradation can differ from a warranty minimum or marketing estimate.
Information you may need
- Usable capacity at installation
- Warranty retention and throughput conditions
- Expected annual cycling and temperature exposure
- Required minimum backup performance over time
Your next step
What to do next
Model runtime at both initial and warranted end-of-life capacity, then ask the provider how capacity is measured and what remedy applies if it falls below the warranty threshold.
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