Charging cycle

A charging cycle describes a complete process of charging and discharging a battery or a Battery Energy Storage System (BESS). The number of possible charging cycles is a key indicator of the service life and quality of a storage system.

How it works

A cycle can either be understood as 100% charging followed by 100% discharging — or as several partial cycles that together add up to one full cycle (e.g. two 50% discharges = 1 cycle).

With each cycle, the battery ages slightly, which over time leads to a reduction in available capacity.

Depending on the cell chemistry and the usage scenario, a storage system can complete several thousand charging cycles.

Typical applications

• Calculation of the expected service life of a Battery Energy Storage System (BESS) (e.g. 6,000 cycles = approx. 15 years with daily use)
• Planning of maintenance or replacement investments
• Design of PV storage systems in commercial and industrial applications
• Evaluation of second-life batteries based on the number of completed cycles
• Optimization of cycle life through charging strategies (e.g. shallower depth of discharge)

Key figures

• Cycle life: number of possible charging cycles until the defined remaining capacity is reached (e.g. 80%)
• Depth of Discharge (DoD): the lower the discharge per cycle, the longer the service life
• Capacity loss per cycle: typical value for high-quality lithium-ion systems: < 0.05%
• Temperature dependence: high temperatures can significantly reduce the number of cycles
• Number of cycles vs. calendar age: the battery also ages even without active use

Summary

The charging cycle is a fundamental unit for evaluating the durability of a Battery Energy Storage System (BESS). The higher the number of possible cycles, the more durable and economical the system is.

Optimized operational management — for example moderate discharging and good temperature management — can significantly extend cycle life.