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Even with excellent Operations & Maintenance, a critical factor influencing long-term BESS performance and profitability is battery degradation — the natural and unavoidable process where a battery’s ability to store and deliver energy gradually decreases over time.

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What Is Degradation?

Degradation in a BESS primarily means one thing: reduced energy capacity. The battery can store less total electricity (fewer MWh) over time. Think of it as the fuel tank shrinking gradually.
Crucially, the power capacity (MW) of a BESS generally remains fixed throughout its life. The asset can still deliver its full power output, but for a shorter duration because it holds less energy. The “engine size” stays the same; the “fuel tank” gets smaller.
This decline happens due to complex chemical and physical changes within battery cells that occur both over time — even when the battery is not being used (calendar aging) — and with usage (cycle aging).

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Factors That Accelerate Degradation

While degradation is unavoidable, certain operational choices can significantly accelerate it. Each creates a fundamental trade-off for asset owners:
  • Cycling (usage): Every charge/discharge cycle causes a tiny amount of wear. More cycles generally mean faster degradation. High usage can generate high short-term revenue, but it consumes the battery’s cycle life faster — potentially shortening its operational lifespan.
  • Depth of discharge (DoD): How much of the battery’s capacity is used in each cycle. Discharging from 100% to 10% (deep cycle) causes more degradation than cycling between 60% and 40% (shallow cycle).
  • Temperature: Operating outside the optimal temperature range — too hot or too cold — significantly accelerates degradation. This is why sophisticated thermal management systems are critical at a BESS site.
  • High power / fast charging: Pushing electricity in or out very quickly puts more stress on battery cells.
  • State of charge extremes: Keeping batteries at very high (near 100%) or very low (near 0%) states of charge for extended periods also contributes to degradation.

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Managing Degradation for Long-Term Profit

How degradation is managed is vital for securing strong financial returns over the asset’s life.
  • Maximising lifetime capacity: Better degradation management — through optimised usage, temperature control, and SoC management within warranty limits — preserves more energy capacity for longer.
  • Sustaining performance: More available capacity means the BESS can perform better and for longer durations, translating directly to more revenue opportunities.
  • Financial planning: All financial models for a BESS asset include an expected revenue-generating lifetime based on anticipated degradation. Smart operational management aims to extend this timeline as far as possible.
It is important to remember that a battery reaching its “end of life” does not mean it stops working entirely. It typically means its energy capacity has degraded to the point where operating costs exceed revenue. Minimising degradation at the lowest possible cost pushes this economic end of life as far into the future as possible — maximising the total return on the investment.
Last modified on April 20, 2026