Path-Q Solar
How does battery degradation change the amount of backup available over time?
Answer
As a battery degrades, its usable energy capacity generally declines, so it can run the same loads for less time or support fewer loads for the same outage. The inverter's power capability may remain sufficient while the energy-duration capability falls, and the actual decline should be evaluated against the manufacturer's retained-capacity warranty.
Key points
- Capacity degradation affects duration; power limits affect how much can run simultaneously.
- Usable capacity depends on reserve settings, depth-of-discharge limits, temperature, and controls.
- Compare beginning-of-life and warranted end-of-life usable capacity.
- A system may still be useful after degradation, but its backup priorities may need to change.
What it depends on
- The battery's capacity-retention specification
- Cycling, temperature, depth of discharge, and operating controls
- The essential-load profile and desired backup duration
Risks and trade-offs
- Sizing only for current capacity can produce inadequate backup later.
- Maintaining a larger reserve may extend useful operation but reduce immediately available energy.
- Replacing a battery or adding capacity may require compatible equipment and additional installation work.
Information you may need
- Beginning and warranted end-of-life usable capacity
- Expected cycling and environmental conditions
- A future-year backup simulation using the essential-load profile
Your next step
What to do next
Ask for an end-of-warranty backup calculation, not just a beginning-of-life rating, and verify which capacity figure is guaranteed.
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