Cycles

General Description

In the battery industry, the concept of a "cycle" is fundamental to understanding battery health and performance. A cycle refers to a complete discharge and recharge process of a battery. However, in real-world applications, batteries rarely undergo full cycles. Instead, they experience partial cycles of varying depths.

To quantify these partial cycles, the concept of Equivalent Full Cycles (EFC) is often used. An EFC represents the amount of charge a battery has cycled relative to a full cycle. For example, a battery that charges from 50% to 100% State of Charge (SoC) and then discharges back to 50% has experienced 0.5 EFC.

However, EFC is only one way to define cycles. There are also other definitions which are used from time to time. One additional definition that is sometimes used is Equivalent Energy Cycles (EEC), which are based on energy throughput and not on ampere hour throughput as it is used for EFCs.

The graph below makes the concept more clear for EFC. It makes clear that one full EFC includes a combined SoC swing of 200%. One full charge and one full discharge swing. However, partial swings can also be used to calculate EFCs.

TWAICE Cycles Calculation

In principle, the calculation of cycles is straightforward, since it is mainly about adding up charge or energy over time. However, data quality oftentimes makes the processing more complicated. Hence, TWAICE includes several pre-processing steps to ensure correct calculations.

The TWAICE Data Pipeline and the data interaction algorithms are used to get from unsorted unclean data to processed, clean and aligned data. This is done since bad data preprocessing can easily corrupt throughput and cycle calculations because small errors add up over a lifetime and become significant

1. Data Preprocessing:

   • Ensure data quality and accuracy.

   • Address missing data or outliers.

   • Calibrate data to account for measurement errors.

2. Charge Throughput Calculation:

   • Integrate the current over time to determine the total charge or discharge.

3. Energy Throughput Calculation:

   • Multiply the current by the voltage and integrate over time to determine the total energy.

4. Cycle Counting:

   • Employ algorithms like the Rainflow Counting Algorithm to identify cycles of varying depths.

Data Preprocessing:

Charge Throughput Calculation:

Energy Throughput Calculation:

Cycle Counting:

What you can do with the TWAICE cycles?

Keeping an Eye on Warranty and Performance Guarantees

Many battery contracts include provisions related to cycle life. By tracking cycle data, compliance with warranty terms is ensured and potential warranty claims can be identified. Check the TWAICE Warranty Tracker and keep an eye on the EFC for the different components and systems to ensure compliance with warranty conditions.

Identify Performance Optimization Potential

Analyzing cycle data makes it easy to identify components that are either less operated compared to other components, potentially due to performance issues, which then in turn leads to other components being heavily stressed since they need to make up for the underperformance of other components. Use the TWAICE Health solution to identify components in the lowest EFC bin and then use TWAICE Performance Manager and System Monitoring to identify root-causes.

Tracking Charge-Discharge Asymmetry

Imbalances between charge and discharge cycles can negatively impact battery health. By monitoring this asymmetry, potential issues can be identified. Use the TWAICE Data Explorer to plot for example for example "TWAICE String Energy Throughput discharge (daily)" and "TWAICE String Energy Throughput charge (daily)". These should be as symmetric as possible. Deviations in the symmetry can be due to losses and inefficiencies.