Before you start reading!
For an introduction to Li-ion battery fundamentals, see our article “Basic Battery Concepts and Qualities.”
This study, Simplified Battery Degradation Calculation, was prepared by Ratio Enerji specialists to give a high-level idea of how to estimate degradation—especially for LFP batteries. Real-world aging is far more complex and normally requires detailed simulations and engineering analysis. Ratio Enerji A.Ş. accepts no liability for decisions made based on this document. For more information, visit ratiosim.com or e-mail contact@ratioenergy.co adresinden uzmanlarımız ile iletişime geçebilirsiniz.
Simplified Battery Degradation Calculation
1. Introduction
When you request a quotation from a battery manufacturer or EPC, you often see concise lifetime statements such as:
Depending on how transparent the supplier is, you may receive only that single line— or pages of cycle-life tables. Yet even the longest tables omit several critical parameters.
This article covers:
- How to read manufacturer degradation data correctly
- Which extra data you must request during tender negotiations
- How to run a quick, back-of-the-envelope degradation check when data remain incomplete
2. What Exactly Is Battery Degradation?
In our earlier articles we explained the physio-chemical mechanisms; here we focus on aspects that matter most to plant owners and operators. Li-ion degradation has two broad components:
- Usage-Based Aging (Cycle Aging)
- Time-Based Aging (Calendar Aging)
2.1. Usage-Based Aging (Cycle Aging)
Usage-based aging lets you track how much a battery’s lifespan shortens and how far its effective capacity declines with each cycle. The key point to remember is that not all cycles are equal:
- A cycle at 25 °C vs. one at 40 °C
- A shallow cycle from 50 % → 90 % → 50 % SoC vs. a deep cycle from 10 % → 50 % → 10%
- A cycle after a long rest vs. one performed an hour after the previous cycle
Each stresses the cell differently. Manufacturers therefore (or should) supply tables similar to the one below.
Table 1: Sample degradation table (actual data has been changed for privacy reasons)
In more basic preliminary proposal documents, the figure is presented in aggregate—e.g., 6 000 cycles @ 1 C” or “8 000 cycles @ 0.5 C and so on—and rests on the assumption that every cycle will occur under roughly similar conditions.a dayanır.
2.2. Time-Based Aging (Calendar Aging)
Just like any other asset, batteries undergo calendar-life deterioration that occurs independently of use. A Li-ion system purchased today will no longer deliver the same performance and efficiency two years from now—even if it has never been operated.
Because Li-ion batteries in most grid-scale applications cycle at least once or twice a week, the capacity loss caused by calendar aging is negligible compared with that from cycle aging. Manufacturers therefore tend to supply only a simplified figure such as “10-year shelf life” instead of detailed calendar-aging data.
In this article we provide a straightforward calculation of degradation based on cycle count and deliberately leave calendar aging out of scope.
3. What Should a Complete Degradation Specification Contain?
3.1. Why a “Single-Line” Lifetime Is Never Enough
Degradation depends on a multidimensional set of variables (temperature, current, dwell time, chemistry). A line like “SOH@EOL = 60 % (20 yrs, 1 cycle day-¹)” cannot capture this complexity.eterli değildir.
3.2. Necessary Parameters for a Complete Degradation Calculation
If your supplier does not provide this data, insist on getting it in writing during warranty/SLA negotiations. Without it, warranty claims are effectively unenforceable..
3.3. The Pitfall of Assuming Linear Degradation
Real degradation follows three phases:
- Early phase (first 100–1 000 cycles): rapid chemical stabilization loss
- Middle phase: approximately linear decline
- Late phase (approaching EoL): accelerated loss from electrolyte breakdown & SEI thickening
A single figure like “7 300 cycles → EoL” hides these phases.
3.4. Efficiency Feedback Loop
SoH düştükçe hücre iç direnci artar, dolayısıyla verimlilik azalır. Aynı net enerji için bataryaya giren-çıkan brüt enerji artar → çevrim sayısı fiilen yükselir → eskime hızı daha da hızlanır.
3.5. Solution: Cycle-Based Simulation with RATIO SIM
RATIO SIM examines every cycle individually as it:
- reads the instantaneous DoD, temperature, C-rate, and rest duration,
- applies chemistry-specific aging functions,
- factors in the efficiency-to-SoH feedback loop, and
- generates realistic, multi-year capacity-loss and warranty-verification reports.
This delivers a quantitative, traceable, and reliable foundation for the bankable feasibility documents required by lenders and for the warranty specifications to be signed with the EPC.
4. Simplified Degradation (Aging) Calculation
During the preliminary-quotation stage most manufacturers do not share full aging curves. Even so, you can perform a quick “back-of-the-envelope” calculation to compare offers or produce a rapid pre-feasibility assessment.
The steps below form a practical method when all you have is the total cycle count and end-of-life (EoL) state-of-health (SoH). As an example, let’s take a battery with a rated energy of 100 MWh. To estimate its usage-based aging we adopt the following assumptions.
During the preliminary-quotation stage most manufacturers do not share full aging curves. Even so, you can perform a quick “back-of-the-envelope” calculation to compare offers or produce a rapid pre-feasibility assessment.
The steps below form a practical method when all you have is the total cycle count and end-of-life (EoL) state-of-health (SoH). As an example, let’s take a battery with a rated energy of 100 MWh. To estimate its usage-based aging we adopt the following assumptions.
4.1. Assumptions
4.2. Effective Capacity on Day 1
- E_eff,0 = Rated Energy × DoD × Efficiency
- E_eff,0 = 100 MWh × 0.90 × 0.90 = 81 MWh
4.3. Effective Capacity at EoL
- E_eff,EoL = E_eff,0 × SoH_EoL
- E_eff,EoL = 81 MWh × 0.60 = 48.6 MWh
So 40 % of the day-one effective capacity is lost over life.
4.4. Average SOH Loss per Cycle (linear approximation)
ΔSOH_total = 100 % – 60 % = 40 %
ΔSOH_cycle ≈ 40 % / 6 000 ≈ 0.0067 % per cycle
- If you operate 1 cycle day-¹, expect ~0.0067 % SOH drop daily.
- At 2 cycles day-¹, double the value, and so on.
Remember: true aging is not perfectly linear!
4.5. How to Use This Quick Method
- Compute ΔSOH / Total Cycles for each supplier.
- Compare linearised ageing rates—assuming identical DoD, temperature, and C-rate.
- Before signing, demand full temperature/DoD/C-rate data and validate with a detailed model (e.g., RATIO SIM).
5. Capacity Criterion in Turkish Energy Regulations
Deliverable Capacity: ≥ 85 % by Year 5 — ≥ 80 % thereafter
Under paragraph 2 of Article 81/A—added to the Regulation Amending the Electricity Market Balancing and Settlement Regulation (DUY):
Here “capacity” is not the battery’s SoH; it is the ratio of the active energy the battery can supply to the grid to the AC power stated in its licence agreement.
The examples below use identical assumptions—DoD 5 %–95 % SoC, round-trip efficiency 90 %, and, unless otherwise noted, 1 cycle day⁻¹—to illustrate scenarios that either fail to meet or are likely to satisfy these regulatory limits.gösterir.
5.1. Basitleştirilmiş Eskime Hesabı – Vaka Çalışmaları
Shared Assumptions
- SoC window: 5 %–95 % (DoD = 90 %)
- Round-trip η = 90 %
- SOH@EoL = 70 %
- Cycle life: 7 000 cycles @ 1 C (Examples 1-2) / 10 000 cycles @ 0.5 C (Example 3)
- Formula (Day 1) : Effective Capacity = DC_Energy × DoD × η
Example1 — 10 MW / 10 MWh
❗ Not compliant — below 85 % from day 1
Example2 — 10 MW / 12.35 MWh
⚠️ Borderline — meets 85 % for 5 yrs but drops below 80 % after year 13.
Example2 — 10 MW / 24.7 MWh (0.5 C, 2 half-cycles day-¹)
✅ Compliant — oversize & lower C-rate keep capacity well above limits.
5.2. Key Takeaways
- Ignoring DoD × efficiency can cause immediate non-compliance (< 85 %) even on day 1.
- Oversizing DC-MWh eases compliance but raises CAPEX.
- Lower C-rate (energy-oriented design) reduces per-cycle stress → slower degradation.
- Real projects should use a full thermo-electro-chemical model and base warranties on that model.
6. Key Points to Remember
- Demand full degradation data (temperature, DoD, C-rate, rest periods, SOH curve).
- Never rely on a single-line lifetime claim.
- Use back-of-the-envelope checks for fast screening, but validate with a cycle-level simulation before signing.
- Ensure designs meet local regulatory thresholds (e.g., 85 % / 80 % in Turkey).
- Consider oversizing or lower C-rate strategies when compliance margins are tight.