Quick Summary
- Battery degradation varies significantly depending on battery chemistry, vehicle type, operating pattern, charging behaviour and environmental conditions.
- Fleets should establish a battery-health baseline from day one. Operators without an existing baseline should independently assess their batteries now to understand their current position.
- VEV also recommends adopting an initial charging/operating strategy that will protect battery health which is battery chemistry dependant
- In one fleet analysed by VEV SOH had reduced by over 8 percentage points in less than 2 years.
- State-of-charge discrepancies can reach as high as 20% above or below the reported figure your driver sees on the dashboard meaning your drivers could be at further risk of running out of charge
- These differences may not stop a vehicle operating today, but they can affect route allocation, charging decisions, vehicle availability and whole-life cost.
- VEV recommends analysing battery performance from day one, establishing a vehicle-level baseline and monitoring changes throughout the vehicle’s life – rather than waiting for a fault to develop.
There is no single battery degradation rate
There is a lot of conflicting information in the market about electric vehicle battery degradation.
Some sources suggest that modern batteries will comfortably outlast the vehicle. Others warn that intensive charging, high mileage and demanding duty cycles could significantly reduce battery life.
The reality is that there is no single degradation rate that applies to every fleet.
Battery performance depends on several interacting factors, including:
- Battery chemistry
- Battery size and usable capacity
- Vehicle efficiency
- Annual energy throughput
- Depth of discharge
- Charging frequency and power
- Operating temperature
- Payload and route profile
- Battery thermal management
- The accuracy of the battery management system
This does not mean fleets should be worried about operating electric vehicles. It means that battery health should be measured using real vehicle data rather than assumed from a generic industry average.
What are state of health and state of charge?
Two battery measurements are particularly important for fleet operators.
State of health, or SoH, describes the battery’s current usable capacity compared with its usable capacity when new.
how about this: For example, a battery with 500kWh of usable capacity when new would be expected to retain around 450kWh at 90% SoH, although calculation methods vary between manufacturers.
State of charge, or SoC, describes how much energy the battery is estimated to contain at a particular moment.
SoH is therefore a longer-term measure of battery condition. SoC is the operational figure used to determine whether a vehicle is ready for its next journey.
Both are normally estimated by the vehicle’s battery management system. While modern BMS (Battery Management System) technology is generally robust, SoH and SoC are calculated values rather than simple physical measurements. Sensor inaccuracies, changes in cell characteristics, temperature and model assumptions can all influence the result.
For a commercial fleet, an inaccurate estimate can become an operational and financial problem.
What we found in a real electric fleet
VEV recently assessed battery performance across an operational electric fleet that had been running for approximately two years.
The average reduction in reported state of health was approximately 4.5 percentage points.
The largest reduction observed on an individual vehicle was 9 percentage points over the same period. This was approximately twice the level previously expected by the operator.
In isolation, this does not make the affected vehicle unusable. A vehicle retaining more than 90% of its original usable battery capacity may still be able to complete every route currently allocated to it.
The important issue is what the result means for the vehicle’s future.
If degradation continues more quickly than assumed in the original business case, that vehicle could reach 80% or 75% SoH several years earlier than planned.
At that point, the vehicle may remain mechanically reliable and commercially useful, but it may no longer be suitable for the longest or most energy-intensive routes in the fleet.
That changes how the asset needs to be managed.
Battery degradation becomes a scheduling issue
Electric drivetrains have the potential to operate over long asset lives. Maximising that value requires the vehicle to remain productively deployed even as its usable battery capacity gradually reduces.
This means route scheduling should evolve alongside battery health.
Imagine a delivery fleet containing a mixture of new and older electric vehicles.
The newest vehicles, with the greatest usable battery capacity, could be prioritised for routes covering more than 150 miles.
Vehicles with lower SoH could be allocated to shorter routes . They may no longer have their original maximum range, but they can still complete those duties comfortably and return with an appropriate operational reserve.
The objective is not to remove an older vehicle from service as soon as its battery degrades.
It is to put the right vehicle on the right route based on its actual capability.
This approach can:
- Extend the productive life of the vehicle
- Reduce premature battery or vehicle replacement
- Protect route completion
- Improve confidence in dispatch decisions
- Support more accurate residual-value forecasting
- Strengthen the whole-life TCO case for electrification
In this model, battery data becomes an input into daily and strategic scheduling.
State-of-charge accuracy can be just as important
Long-term degradation is only part of the battery-health picture.
In the same fleet analysis, VEV identified vehicles that were misreporting state of charge on an intermittent basis. Wider industry analysis has observed, differences of up to 20 percentage points above or below the expected SoC were also identified.
Five percent may not sound significant. But on a vehicle with a 500kWh battery, it represents 25kWh of energy which could be 20km of range in larger vehicles or 64km in vans
The distance represented by that energy depends on the vehicle’s efficiency, payload, weather and route. However, it can be the difference between completing a shift confidently and requiring an unplanned charging stop.
An SoC discrepancy can create problems in either direction.
When SoC is overreported
The fleet team may believe that the vehicle has more energy available than it actually does.
This can result in:
- A vehicle being assigned to an unsuitable route
- A reduced operational safety margin
- An unexpected mid-route charging requirement
- A vehicle returning with critically low energy
- Service disruption or missed deliveries
When SoC is underreported
The vehicle may have more energy than the operating team believes.
This can lead to:
- Unnecessary charging
- A vehicle being held at the depot for longer than required
- Avoidable charger occupation
- The unnecessary reassignment of routes
- Reduced fleet availability
- Poor charging and energy forecasts
The vehicle’s protection systems should prevent unsafe overcharging. However, inaccurate operational information can still cause the fleet to make inefficient decisions about when a vehicle should charge and when it is ready to leave.
Do not rely on the fleet average
A fleet-level average can hide the vehicles that require attention.
An average SoH reduction of 4.5 percentage points may initially appear manageable. But that headline does not show the difference between a vehicle that has lost 2% of its usable capacity and one that has lost more than 8%.
The same applies to SoC accuracy.
A fleet may appear broadly accurate while a small number of vehicles repeatedly report materially incorrect figures.
Battery monitoring should therefore work at individual-vehicle level and identify:
- Vehicles degrading faster than comparable assets
- Sudden changes in reported SoH
- Differences between indicated SoC and observed energy use
- Unusual charging curves
- Unexpectedly low energy acceptance
- Cell or module imbalance indicators, where available
- Differences between energy delivered by the charger and energy recorded by the vehicle
- Changes in efficiency that cannot be explained by route, payload or temperature
The objective is to identify exceptions early, before they affect operations or asset value.
Battery monitoring should also support safety
Fleet data can help identify battery behaviour that warrants further investigation.
For example, operators can compare the manufacturer’s stated battery capacity with the usable energy observed during charging and operation. They can also monitor changes in temperature, charging performance, energy acceptance and efficiency.
However, operational analytics should not be treated as a replacement for an OEM diagnostic, workshop inspection or specialist battery assessment.
Its role is to provide an early-warning system.
Where the data identifies a significant or unexplained anomaly, the vehicle should be escalated for appropriate technical investigation. This allows fleet teams to move from reactive fault management to evidence-led preventative maintenance.
What should fleet operators do?
VEV recommends that fleets operating electric vehicles for more than two years begin a structured battery-health assessment.
This should include five practical steps.
- Establisha vehicle-level baseline – Record the reported SoH, usable battery capacity, charging behaviour, efficiency and operating profile of each vehicle. The earlier this baseline is created, the easier it becomes to identify deterioration or unexpected changes.
- Validate vehicle data against other systems – Compare information from the vehicle with charger data, telematics, route mileage and measured energy consumption. No single data source should be assumed to be completely accurate.
- Monitorthe trend, not just the latest figure – A single SoH or SoC reading may be misleading. Fleet teams should look for persistent differences, sudden changes and vehicles that are moving away from the performance of comparable assets.
- Incorporate battery health into route allocation – Use known battery capability when assigning vehicles to routes. Prioritise higher-SoH vehicles for longer or more energy-intensive duties and retain lower-SoH vehicles on shorter, predictable routes where they can continue to operate productively.
- Update the whole-life business case – Actual degradation should feed back into replacement planning, warranty management, residual-value assumptions and TCO modelling. This allows decisions to be based on the fleet’s real battery performance rather than the degradation rate assumed when the vehicles were purchased.
The bottom line
Battery degradation should not be viewed as a reason to delay fleet electrification.
It should be viewed as an asset-management challenge.
The vehicles in the VEV analysis were still capable of completing their required routes. But the differences in state of health and state-of-charge accuracy showed why fleets cannot simply deploy electric vehicles and assume the original operating plan will remain appropriate throughout their lives.
The real opportunity is to use battery data to continually adapt the fleet.
A vehicle does not become worthless because it can no longer complete the longest route. It may still have many productive years available on a shorter or less energy-intensive duty.
By monitoring SoH, validating SoC and incorporating battery capability into scheduling, operators can protect uptime, extend vehicle life and maximise the return on their investment.
Because the objective is not simply to make an electric vehicle last.
It is to keep every vehicle doing the most valuable job it is capable of doing throughout its life.
To learn more about how VEV can assess battery health, vehicle performance and the ongoing optimisation of your electric fleet, contact us at ask@vev.com.
*All statistics are from VEV’s own and partner analysis
19 August 2026
