From FAT to COD: Why Battery Storage During Transport and Commissioning Matters

A container of LFP batteries stored at 30°C for 90 days before COD loses 0.8–1.2% SOH before it ever cycles — equivalent to losing $160,000–$240,000 of usable capacity on a 200 MWh system at $200/kWh.

That loss happens whether the battery is on a ship crossing the Pacific, sitting in a port warehouse, or waiting on a concrete pad for the commissioning engineer to arrive. It is not a warranty claim. It is not a manufacturing defect. It is simply calendar aging — the same electrochemical process that drives degradation over 25 years of operation, concentrated into a few months of preventable inaction.

Most BESS project teams fixate on degradation during the operational phase. They model the fade curves, plan augmentation schedules, and negotiate throughput warranties. But the clock on battery degradation starts ticking the moment the cells leave the factory floor. The period between Factory Acceptance Test (FAT) and Commercial Operation Date (COD) is a hidden erosion of project value that rarely appears in financial models — and it can cost hundreds of thousands of dollars per project.

This article breaks down the FAT-to-COD degradation problem, introduces Energy Optima's dedicated calculator for quantifying these losses, and provides best practices to protect against pre-COD capacity erosion.

The FAT-to-COD Degradation Problem

Between the moment a battery module passes its factory acceptance test and the day it begins commercial operation, the asset goes through a complex logistics and commissioning chain. During this period, the battery is typically stored at ambient temperature, often at a high state of charge, and frequently without climate control.

Calendar aging does not pause for logistics. The Arrhenius relationship that governs degradation rate at the cell chemistry level applies at every temperature the battery experiences. At 25°C, a typical LFP cell loses roughly 0.02–0.03% SOH per day from calendar aging alone. At 35°C, that rate doubles. Over a 90-day logistics chain, the cumulative loss is measurable in percentage points of SOH — not basis points.

The FAT-to-COD phase is also the one period in a battery's life where the project team has the least visibility into actual conditions. Shipping container temperatures are rarely logged. Warehouse conditions are unknown. Commissioning delays are treated as schedule issues, not degradation events. This blind spot means every financial model built on "100% as-tested SOH at COD" is working from a starting point that has already drifted lower.

For a full walkthrough of FAT, SAT, and COD milestones themselves, see our companion guide BESS Factory Acceptance Test to Commercial Operation: FAT, SAT, and COD Explained.

Three Periods of Pre-COD Degradation

The FAT-to-COD timeline breaks naturally into three distinct degradation periods, each with its own conditions and risk profile:

Shipping

The shipping phase covers the journey from the battery factory to the project port or site. For transoceanic shipments, this can last 30–60 days. Container ships have no climate-controlled cargo holds for containerized battery storage. Internal container temperatures in tropical shipping lanes can exceed 50°C during the day, even with ventilation. At those temperatures, LFP calendar aging rates accelerate 3–5× above the 25°C baseline.

Vibration during shipping does not directly contribute to electrochemical degradation, but it can loosen terminals, stress busbars, and create resistive joints that manifest as increased internal resistance — an effect sometimes misattributed to cycling degradation later in the project life.

Storage

The storage period is typically the longest and most variable. Batteries may sit in a factory warehouse, a port container yard, a trucking depot, or a project laydown area for 30 to 365 days depending on procurement timing, construction schedules, and supply chain coordination.

Calendar aging during storage follows a well-characterized Arrhenius relationship. For LFP chemistry stored at 50% SOC, the daily SOH loss at various temperatures is:

Temperature	Daily SOH Loss (LFP @ 50% SOC)	90-Day Cumulative Loss
15°C	0.007%	0.63%
25°C	0.012%	1.08%
35°C	0.024%	2.16%
45°C	0.045%	4.05%

These rates are for low-SOC storage. At 100% SOC, the rates approximately double across all temperatures due to the elevated chemical potential driving faster lithium inventory loss at the anode SEI layer.

Pre-Commissioning

Once batteries arrive at the project site, the pre-commissioning phase begins. This period involves unpacking, racking installation, DC bus wiring, inverter commissioning, EMS integration, and site acceptance testing. Delays in any of these activities extend the pre-COD period.

The critical variable during this phase is state of charge management. Batteries arriving from the factory are typically shipped at 30–50% SOC per transport safety regulations. But during commissioning, the BMS may charge the battery to higher SOCs for testing, and if the system is not cycled afterward, the battery sits at elevated SOC for days or weeks, accelerating calendar aging.

Commissioning delays of 30–90 days are common in the industry, driven by grid interconnection timelines, contractor scheduling gaps, and regulatory approvals. Each week of delay at elevated SOC adds measurable degradation that reduces the total lifetime throughput of the asset.

Influence Factors: Chemistry, Temperature, SOC, and Duration

Pre-COD degradation is governed by four primary factors. Understanding how each interacts is essential to modeling the loss accurately.

Chemistry: LFP vs NMC Storage Characteristics

LFP and NMC chemistries exhibit fundamentally different calendar aging behavior during storage. LFP benefits from a flat voltage curve and lower chemical potential at comparable SOCs, which translates to slower calendar aging. NMC, with its higher energy density and higher nominal voltage, loses capacity faster under identical storage conditions.

At 25°C and 50% SOC, typical calendar aging rates are:

• LFP: 0.010–0.015% SOH loss per day
• NMC: 0.018–0.030% SOH loss per day (1.5–2× higher)
• NCA: 0.022–0.035% SOH loss per day (2–2.5× higher than LFP)

This means the chemistry choice has an immediate impact on how much pre-COD degradation your project will experience. An NMC project with a 90-day logistics chain at 25°C loses roughly 1.6–2.7% SOH before COD — more than double the LFP loss for the same timeline.

Temperature: The Arrhenius Relationship

Battery degradation follows the Arrhenius equation: reaction rates (and therefore degradation rates) increase exponentially with temperature. The rule of thumb is that calendar aging rate approximately doubles for every 10°C rise in storage temperature between 15°C and 45°C.

This has practical consequences for global supply chains. A battery shipped from a factory in Southeast Asia (ambient 30–35°C) and stored in a Middle Eastern port (40–50°C in summer containers) will experience 3–4× the calendar aging of the same battery stored in a climate-controlled European warehouse at 20°C.

SOC During Storage: Lower Is Better

Storage SOC is the most controllable variable in pre-COD degradation management. The calendar aging rate at 100% SOC is approximately double the rate at 30% SOC for both LFP and NMC chemistries. This is because the anode potential at high SOC is more reducing, driving faster SEI growth and lithium inventory depletion.

Industry best practice is to store batteries at 30–50% SOC. Many manufacturers explicitly specify storage SOC ranges in their product documentation. Energy Optima's chemical-specific storage parameters endpoint captures these manufacturer-recommended ranges for 112 batteries across 44 manufacturers, accessible at /api/v1/chemical-storage-params.

Duration: Non-Linear Effects

Calendar aging is approximately linear with the square root of time, not with time itself. This means the first 30 days of storage account for a disproportionate share of the total degradation. For a battery stored at 25°C, day 1–30 of storage may account for 40–45% of the degradation seen in the first 180 days.

The practical implication: even short pre-COD periods matter. A 30-day logistics chain is not "zero risk." It still produces measurable SOH loss that should appear in the project baseline.

Energy Optima's FAT-to-COD Calculator

Energy Optima provides a dedicated FAT-to-COD degradation calculator at /api/v1/fat-cod that models SOH loss across all three pre-COD periods with chemistry-specific parameters.

Calculator inputs:

• Shipping period: Duration (10–60 days), average temperature (0–50°C), estimated SOC during transport
• Storage period: Duration (30–365 days), average ambient temperature (15–35°C), average SOC during storage
• Pre-COD period: Duration (7–90 days), site temperature (design temperature), average SOC during commissioning
• Chemistry: LFP, NMC, or NCA with configurable storage parameters
• System size: Total MWh capacity at FAT, system cost per kWh

Calculator outputs:

• SOH at COD (compared to 100% at FAT)
• Lost usable capacity in MWh
• Financial impact in dollars based on system cost/kWh
• Breakdown by period showing which phase contributed the most degradation
• Temperature sensitivity analysis

The calculator uses Energy Optima's chemical-specific storage parameters endpoint (/api/v1/chemical-storage-params) to apply the correct Arrhenius coefficients, SOC multipliers, and chemistry-specific calendar aging curves for the selected battery.

For a broader treatment of degradation modeling across the full project lifecycle, including how FAT-to-COD loss feeds into operational fade projections, see our BESS degradation modeling guide.

How Pre-COD Loss Compounds Over 25 Years

The $160,000–$240,000 in lost capacity from a typical 90-day FAT-to-COD timeline is the direct, upfront cost. But the real financial damage is larger because pre-COD loss compounds over the project life.

Consider two identical 200 MWh LFP projects, both with the same operational degradation trajectory of 2%/yr. Project A starts at 100% SOH at COD. Project B starts at 99% SOH at COD due to a 90-day storage period at 30°C.

The difference is not static. Here is how it plays out:

• Year 0: Project B has 2 MWh less usable capacity ($400,000 at $200/kWh)
• Year 10: Project A at ~80% SOH has 160 MWh usable; Project B at ~79% has 158 MWh usable — the 2 MWh gap persists because both fade at the same rate from different starting points
• Year 25: Project A delivers ~1,460 GWh of lifetime throughput; Project B delivers ~1,445 GWh — a 15 GWh lifetime shortfall

The 15 GWh of lost throughput at an average revenue of $30/MWh represents $450,000 in revenue that Project A captures and Project B does not. When discounted at 8% over 25 years, the net present value of the lost capacity is approximately $100,000 per 0.5% of upfront SOH loss.

This compounding effect is why pre-COD degradation management belongs in the project financial model, not just the logistics spreadsheet. Every degree of temperature avoided and every week of delay compressed during the FAT-to-COD timeline protects the project's lifetime NPV.

When pre-COD losses push a project past its augmentation trigger earlier than planned, the costs multiply. For the relationship between SOH triggers and augmentation planning, see our battery augmentation planning deep dive.

Best Practices to Minimize FAT-to-COD Degradation

Pre-COD degradation is not inevitable. Project teams can take specific actions during each phase to reduce calendar aging and preserve SOH.

During Shipping

• Specify temperature-controlled containers for transoceanic and overland shipping of battery systems, especially for NMC projects where the per-day degradation rate is highest
• Ship at reduced SOC — target 30% SOC rather than 50%. The 20 percentage point SOC reduction cuts calendar aging by approximately 25–30%
• Minimize intermediate stops — each port transfer and customs hold adds unmonitored calendar aging time. Direct routing reduces uncertainty
• Log container temperature — deploy low-cost data loggers inside shipping containers to obtain actual temperature exposure data for post-COD degradation analysis

During Storage

• Use climate-controlled warehousing — a 15–20°C warehouse halves the calendar aging rate compared to ambient storage at 30°C
• Monitor SOC monthly — self-discharge and BMS quiescent loads can drift SOC downward over months. Re-conditioning to target SOC before it falls too low prevents the need for a full charge cycle that would temporarily elevate SOC
• Store at 30–50% SOC — this is the manufacturer-recommended sweet spot for most LFP and NMC cells
• Track storage duration — project schedules should include a "battery storage timer" that alerts the team when any container has been in storage beyond the modeled timeline

During Pre-Commissioning

• Cycle batteries during commissioning delays — if grid interconnection is delayed, use the battery's inverter to perform partial charge/discharge cycles. This does not eliminate calendar aging, but it prevents the battery from sitting at a fixed elevated SOC for weeks
• Keep SOC at 30–50% during commissioning pauses — after any commissioning test that charges the system above 50%, cycle the battery back down before leaving it idle
• Rent temporary cooling — for outdoor installations, containerized HVAC or shade structures reduce internal container temperatures by 10–15°C compared to direct sun exposure
• Include SOH verification in SAT — measure SOH during site acceptance testing to establish the actual baseline for the operational phase

Putting It Into Practice

Pre-COD degradation is a hidden variable in most BESS financial models, but it does not have to be. With Energy Optima's FAT-to-COD calculator and chemical-specific storage parameters, project teams can:

• Quantify the SOH impact of every week of logistics and commissioning delay in dollars
• Compare storage scenarios — climate-controlled vs ambient, 30% vs 50% SOC, short vs extended timelines — to optimize the tradeoff between logistics cost and capacity preservation
• Start 25-year operational degradation projections from the correct COD baseline instead of an idealized 100% SOH
• Include pre-COD loss in investor reporting and debt financing models for full transparency

The battery's degradation clock starts ticking at FAT, not COD. The difference between those two dates is a window of preventable capacity loss that compounds into millions of dollars of lifetime value. The mathematics of calendar aging are well understood. The only question is whether your project model accounts for them.