About the Cycle Life
Cycle life is the number of complete charge-discharge cycles a battery can perform before its capacity degrades to a specified end-of-life threshold (typically 80% of original). It is the primary durability metric for BESS economics — directly determining how often the battery must be replaced and the true LCOS.
Formula
Effective years = Cycle life ÷ Annual cycles
- Cycle life
- Rated cycles to 80% capacity at the specified DoD (e.g. 4,000 cycles at 80% DoD for LFP)
- Annual cycles
- Number of charge-discharge cycles per year (1 cycle/day = 365/year)
Throughput (kWh) = Cycle life × Nameplate × DoD × Round-trip efficiency
- Throughput
- Total lifetime energy delivered by the battery (kWh)
How to calculate it
- 1Identify the use case: daily cycling (peak shaving, solar+storage) = ~365 cycles/year; seasonal backup = ~50–100 cycles/year.
- 2Match battery chemistry to cycle demand: LFP for high-cycling applications (4,000–6,000 cycles), NMC for lower-cycle applications.
- 3Calculate effective calendar life: cycle life ÷ annual cycles.
- 4If calendar life > expected project life, no replacement is needed — the battery outlasts the project.
- 5If calendar life < project life, budget for replacement and include it in LCOS.
Worked example
LFP battery, 4,000 cycles at 80% DoD, used for daily solar peak-shifting (365 cycles/year): effective life = 4,000 ÷ 365 = 11 years. A 25-year project would need one replacement at year 11. Total throughput = 4,000 × 100 kWh × 0.80 × 0.93 = 2.98 L kWh per battery pack.
What you can calculate
- Cycle count
- DoD vs life
- LFP/NMC
- Calendar years
Frequently asked questions
What is the cycle life of a typical BESS in India?
LFP (the dominant chemistry for Indian utility and C&I storage): 4,000–6,000 cycles to 80% capacity at 80% DoD. NMC: 1,000–3,000 cycles. Lead-acid (VRLA): 400–800 cycles at 50% DoD. At one cycle/day, LFP lasts 11–16 years before replacement; lead-acid typically needs replacement every 2–4 years — a major driver of LFP's lower LCOS despite higher initial cost.
Does temperature affect battery cycle life?
Yes significantly. LFP cells have optimal cycle life at 20–35°C; above 40°C, cycle life degrades noticeably. Indian summers can push battery enclosure temperatures above 45°C without active cooling, accelerating degradation. BMS thermal management, HVAC or active ventilation, and siting batteries in shaded or insulated enclosures are critical for achieving rated cycle life in Indian conditions.
What is a full cycle vs a partial cycle?
A full cycle is a complete discharge from 100% SoC to the minimum SoC and back. Partial cycles (e.g. 20% discharge each time) are gentler — battery manufacturers often rate cycle life in cumulative throughput (kWh) rather than raw cycles, because 5 shallow 20% cycles use the battery equivalently to 1 full 100% cycle.
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