Cycle Life
Cycle Life is the number of complete charge-and-discharge cycles a rechargeable battery cell, module, or energy storage system can complete under specified depth of discharge (DoD), C-rate, and temperature conditions before its usable capacity falls to its end-of-life (EOL) State-of-Health threshold, typically 70% or 80% of nominal beginning-of-life capacity.
How it is measured and specified
A cycle-life figure is meaningful only when paired with four laboratory boundary conditions: cell or module temperature, charge and discharge C-rate, depth of discharge (DoD), and the State-of-Health (SoH) retention percentage that defines end of life. In commercial lithium iron phosphate (LFP) stationary storage datasheets, manufacturers normally test cells at a controlled ambient temperature of 25±2°C, a standard charge and discharge rate of 0.5C, an 80% to 90% DoD window, and an EOL knee of 70% or 80% retained capacity.
In real field operation, total degradation combines cyclic fade (driven by lithium-ion intercalation stress and solid-electrolyte interphase growth during energy throughput) with calendar fade (driven by ambient temperature and average state of charge while idle). Consequently, an LFP rack operating at elevated cell temperatures or higher C-rates reaches its EOL threshold in fewer equivalent full cycles than a brochure curve suggests.
How it matters when sourcing from China
When procuring containerized or cabinet LFP systems from Chinese OEMs—such as CATL EnerC and EnerC+ liquid-cooled containers, EVE LF280K 280 Ah prismatic cells, or BYD Blade and MC Cube storage racks—buyers must separate headline cell cycle ratings from system-level ten- or fifteen-year cash flows. As detailed in how battery and storage TCO is modelled, cycle life and warranty terms remain supplier claims until the datasheet, operating duty profile, and augmentation schedule are bound into the contract.
In high-ambient destination corridors, real duty cycles require explicit degradation and mid-life replacement reserves rather than relying on nominal laboratory curves:
- In the 3 MWh Middle East & Africa hospital ESS TCO study, which references the CATL EnerC 3.72 MWh liquid-cooled LFP container class and BYD MC Cube, the 15-year financial model applies a 2.0%/yr linear capacity fade assumption under hot-climate daily cycling (365 cycles/year at 85% DoD) and budgets a Year-8 cell augmentation and stack replacement reserve equal to 30% of initial battery CAPEX.
- In the 3 MWh India harbor BESS TCO study, where the system dispatches two equivalent cycles per day (2.0 MWh/day throughput across peak shaving, crane regeneration, and shore power), the model incorporates 2.0%/yr capacity fade alongside a Year-8 stack augmentation event.
- Before containers leave the Chinese factory, buyers can establish an objective beginning-of-life baseline using the battery pack capacity-retention test SOP, which cycles sampled LFP packs at 25±2°C and 0.5C under IEC 62619 / GB/T 36276 protocols and requires measured discharge capacity to reach at least 95% of nominal rating before shipment release.
What to confirm before procurement
- Request the OEM's temperature- and C-rate-indexed cycle-life curve alongside the warranty schedule showing both years and cumulative megawatt-hour throughput caps.
- Confirm the exact State-of-Health percentage (70% vs 80% of nominal capacity) that triggers a warranty remedy or requires rack augmentation.
- Specify whether mid-life cell augmentation or DC-block overbuilding is included in the initial FOB/CIF quote or carried as a future capital expense in the project's TCO model.