Battery Degradation
Definition
Battery degradation is the gradual loss of a battery's usable energy capacity, and sometimes its power and efficiency, as it ages and is charged and discharged. It depends on how many cycles the battery runs, how deeply, how fast, at what temperatures and at what states of charge. Fluence describes augmentation as the installation of additional batteries 'to compensate for partially lost capacity due to degradation of batteries over time.'
Why it matters
Degradation turns a battery's capacity into a declining asset, which matters most where revenue is paid on energy delivered. Two projects with similar contracts can have very different cash flows if one assumes slow fade and no augmentation spending. Investors should look for the assumed degradation curve, the cycling it assumes, who pays to restore capacity, and whether a warranty or service agreement covers it.
Common misconceptions
- •Degradation is not a defect. It is expected; the question is the rate and who bears it.
- •A warranty does not cover degradation from operation outside its limits.
- •Year-one capacity is not lifetime capacity, and a flat revenue projection may ignore fade.
- •The label is only a starting point. Investor outcomes usually depend on the governing documents, cash-flow priority, valuation policy, disclosure quality, and manager discretion surrounding the term, not just the shorthand definition used in marketing materials.
Technical details
Drivers
Number of cycles and depth of discharge.
Charge and discharge rate: the Marviken agreement warns that excessive C-rates 'can cause accelerated degradation.'
Temperature.
Time spent at high or low state of charge.
How contracts handle it
Capacity guarantees tested periodically, with damages if capacity falls short (Pelican's Jaw's financing refers to a Tested Capacity Ratio and a Guaranteed Capacity Ratio under its EPC contract).
Service agreements that maintain capacity above a threshold through augmentation.
Operating limits on cycles and state of charge that keep the warranty valid.
How investors apply the term
Investors usually apply this term by tying the definition back to the controlling documents and then asking which cash flows, rights, restrictions, or valuation assumptions it changes. A useful review looks at the term alongside fees, leverage, liquidity, reporting frequency, and manager discretion rather than treating it as a standalone concept.
The practical diligence test is simple: identify who benefits if the assumption is wrong, who has control when conditions change, and what evidence the investor receives after closing. Terms that cannot be reconciled to documents, cash movements, and monitoring data should be treated as marketing shorthand until proven otherwise.
Frequently asked questions
- How does degradation affect long-term cash flow?
- Less usable energy means less to sell in energy markets and, if capacity falls below a contract's guaranteed level, payment reductions or damages unless capacity is restored. Projections therefore assume a degradation curve and the cost of augmentation or replacement to hold capacity.
- What end-of-life point do companies assume?
- It varies by product. Nomad Transportable Power Systems, in financial statements filed by Nomad Power Solutions in September 2026, depreciates its batteries on about 365 operating cycles a year over an estimated 17-year life, about 6,205 cycles, and treats '70.8% of Beginning-of-Life ('BOL') capacity' as the end-of-life threshold.
- Does cycling more always increase returns?
- No. NREL notes that providing multiple services 'may require operating an energy storage technology at suboptimal levels through, for example, increased cycling,' which 'could lead to increased operating costs and accelerated degradation of the technology, reducing its economic lifetime.'
- How is degradation monitored?
- By periodic capacity tests and operating data. In the Marviken battery agreement, the operator must keep a 'Degradation Log' documenting the cumulative effect of trading on battery health; Pelican's Jaw reports capacity test results and degradation to its lenders.