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How to avoid battery degradation in electric buses

Alexander Schabert dives into the many ways to prolong battery life within buses

Public transport is electrifying worldwide. The UK is expected to have the largest eBus fleet in Europe by 2024, with London planning to fully electrify its bus fleet by 2034. Today, one-third of Belfast’s Translink fleet is zero-emission, with plans to decarbonise completely by 2030.

While the total cost of operation (TCO) of an eBus is less costly than that of a diesel long-term, the initial investment in sustainable vehicles can be high. Intelligent fleet monitoring and charge process management tools can reduce the TCO of an eBus further. For example, driving style monitoring tools can help operators identify and reduce idling where possible by training drivers based on concrete action points.

Clean buses
Cities like London are clean to decarbonise their bus fleets

The battery alone represents nearly 50% of the total cost of an eBus. As in the EV world it’s customary to no longer use a battery when it reaches 80% of its original capacity, it’s even more significant to look at battery health. All batteries will inevitably degrade with use, usually due to four main factors: temperature, high power, depth of discharge and the average state of charge.

As with humans, batteries function best at temperatures between 15 and 30 degrees Celsius. High temperatures tend to increase the speed of the ions within the battery, leading to chemical reactions that prevent the ions from doing their job of transporting energy around. Extreme low temperatures also decrease their capacity to store energy. It’s therefore recommended that on hot days, buses are parked in the shade or under an overhead shelter. On very cold days, parking in a garage can help minimise battery degradation.

Secondly, unless batteries are optimised for fast charging, it’s usually best to avoid high power/current when charging or discharging them. High power makes battery cells wear out faster and decreases the overall life expectancy. Therefore, lower current and power requests are generally considered better for batteries.

The battery alone represents nearly 50% of the total cost of an eBus

The third aspect to consider is the depth of discharge (DoD). We can say that going from 0% to 50% to 0% is half of a full cycle, at a DoD of 50%. Charging cycles directly impact the ageing of a battery. The lower the cycle height, the better. In other words, it’s better to get 1,000 charging cycles by charging the battery 2,000 times from 50% to 100% to 50%, rather than charging 1,000 times from empty to full to empty.

The average state of charge (SoC) has an impact on battery health as well. In general, having your batteries stalled or operated close to 100% or to 0% SoC is detrimental to the health of the battery. A best practice is to instead operate batteries at an SoC of 50% on average.

When batteries do inevitably become unusable for public transport, it’s possible to resell them to third parties such as recyclers, to a secondary market or back to the manufacturer. There are also multiple in-house usages, such as for tram and train substations, or in combination with bus charging stations.

The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.

Alexander Schabert is Senior Director of Global Bus at ChargePoint, an electric vehicle charging network operating in North America and Europe

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