Re-purposing of second life batteries is a relatively new activity that has increasingly gained importance and attention in the last years as transport industry swifts from fossil fuels to electrical power. However, there are important difficulties that act as barriers to enter into the business, which is the reason why there are just a handful of companies in the world dedicated to repurposing large electric vehicle batteries.

The main challenges when working with second-life batteries are:

• Determine their state of health
• Predict future performance and ageing
• In case of working at a cell level, deal with imbalances between cells

In this article we will focus on the first challenge: determine the state of health (SoH) of a battery. The SoH of a battery is calculated as the ratio between the actual capacity of the battery and its original capacity when manufactured. It is measured in a percentage basis, so this parameter tells us what percentage of the original capacity is still available in the battery.

Measuring the capacity of a battery is well regulated by international entities like the International Electrochemical Commision (IEC). However, these regulated testing methodologies to determine the capacity of a battery are often difficult to industrialize. Very well controlled ambient conditions, long testing times and high cost are some of the typical impediments.

Moreover, second life batteries have important singularities that condition and limit the effectiveness of standardized procedures, due to the very different past lives of the batteries in terms of using and storing conditions. A battery that comes from an electric car that was used for 7 years in Arizona and stored for 3 years before being reused is very different from another one used in Norway for 5 years that is reused 6 months after being removed from the vehicle.

Therefore, at BeePlanet Factory we needed to develop a proprietary, resource-efficient though precise testing methodology to determine the SoH of batteries in an industrial environment.

Our testing methodology was developed in such a way that we have a core part, common to all the batteries we work with, and a secondary part that is particular to each specific battery. This adaptive testing methodology has proven to be optimal for industrialization, since it gives us the flexibility to work with multiple automotive OEMs faster and with higher precision. When we start a collaboration with a new OEM, we just need to invest some time and resources to fully understand the behavior of those particular batteries and model the secondary part of the methodology.

By making use of this technique, we are able to efficiently sort the received batteries based on their SoH. Depending on the results, we then decide to recycle them or include them in our products, having the certainty that BeeBattery products always provide high performance and comply with the given warranty.

Carlos Larrea
Lead Electrical Engineer at BeePlanet Factory