Battery Degradation Cost Over Time
Like any battery, a home battery loses usable capacity over years of charge cycles, which means its value in year ten is lower than its value in year one. This tool uses an averaged, degradation-adjusted savings figure instead of an optimistic year-one number, for a more honest long-term picture.
At your inputs, the battery, using a degradation-adjusted savings estimate has an NPV of -$10,610 over 10 years, with a discounted payback of no discounted payback within this horizon.
| Net cost after confirmed incentives | $12,000 |
|---|---|
| Annual savings | $180 |
| Net present value | -$10,610 |
Breakeven: No discounted payback occurs within the selected horizon.
- This uses planning estimates you entered, not a contractor quote or guaranteed savings.
- Degradation rates vary by battery chemistry and usage pattern; use your manufacturer's stated warranty capacity retention where available.
What this also tells you: A positive NPV means the option is worth more than its cost even after discounting future savings back to today; a negative NPV means the upfront cost outweighs what the savings are worth today.
This is a planning estimate based on your entries. It does not size equipment, determine electrical or building-code compliance, verify incentive eligibility, or replace a contractor quote or professional energy audit.
Why this decision comes up
Battery sales estimates often lean on first-year performance numbers, which look better than what a homeowner will actually experience averaged across a decade of gradual capacity loss.
How this is calculated
This uses the same NPV math as the other Insight-class tools in this cluster, but asks for a degradation-adjusted average annual savings figure instead of a year-one number, discounted back to today's dollars over your ownership horizon.
A worked example
With the defaults ($12,000 net cost, $1,800/year grid-only cost dropping to a degradation-adjusted $1,620/year average, 10-year horizon, 5% discount rate), the annual savings is $180 and the NPV comes out negative at about $10,610, notably worse than a naive, non-degraded estimate would suggest, which is exactly the honest picture this tool is built to show.
Common mistakes
A common mistake is running every battery calculation with an optimistic year-one savings figure, which overstates the investment's real long-term value once degradation is accounted for.
Limitations
This uses a single averaged degradation figure rather than modeling year-by-year capacity loss explicitly. A manufacturer's stated capacity-retention curve is a more precise source if you want to refine your own estimate.
Common questions
How much do home batteries typically degrade?
It varies by chemistry and usage pattern. Manufacturer warranties commonly guarantee a minimum capacity retention (often 70-80%) at a stated year, which is a more reliable source than a generic assumption.
Why not just use the year-one savings figure?
Because it overstates the battery's average value across its full life. A degradation-adjusted figure, averaged across the years you'll own it, gives a more honest basis for an NPV calculation.
Does a warranty offset this degradation cost?
A capacity-retention guarantee limits how much degradation you'll actually experience, and a replacement or repair guarantee can offset worse-than-expected degradation. See the warranty value tool to price that protection specifically.
Does how deeply I discharge the battery affect its degradation rate?
Yes, consistently discharging a battery very deeply each cycle typically accelerates degradation compared to shallower, more moderate cycling. Check your system's specific operating recommendations for guidance on this.
Does installation temperature affect battery degradation?
Yes, batteries kept in very hot or very cold conditions typically degrade faster than one in a moderate, climate-controlled space. Installation location is a real factor in long-term performance worth discussing with your installer.