Cycle Life

Cycle life is the total number of complete charge-discharge cycles a battery can perform before its capacity degrades to a specified threshold — usually 80% of original rated capacity. It is the primary metric for comparing battery longevity across different chemistries and products.

Cycle life is always stated at a specific depth of discharge because deeper discharges wear batteries faster. A lead-acid battery might be rated for 500 cycles at 50% DoD but only 200 cycles at 80% DoD. LiFePO4 batteries commonly deliver 3,000 to 5,000 cycles at 80% DoD — a massive advantage that drives their dominance in daily-cycling solar applications.

To translate cycle life into years of service, divide by the number of cycles per year. A battery cycled once daily accumulates 365 cycles per year. A LiFePO4 battery rated for 4,000 cycles at 80% DoD would last roughly 11 years with daily cycling. A lead-acid battery rated for 500 cycles at 50% DoD would need replacement in about 1.4 years under the same usage pattern.

Real-world cycle life depends on operating conditions beyond DoD. Temperature extremes, improper charging profiles, excessive charge/discharge rates, and poor maintenance can all reduce actual cycle life below the manufacturer's rated specification. Following the manufacturer's recommended charge parameters and operating temperature range is essential for achieving rated cycle life.

When evaluating batteries, always compare cycle life at the same DoD. A battery claiming 2,000 cycles at 30% DoD is not necessarily better than one claiming 1,500 cycles at 80% DoD — the latter delivers far more total energy throughput over its lifetime.