Slide 1. Introduction.
The class develops the degradation of plug-in hybrid batteries and the implications for fleet management.
Slide 2. The degradation of plug-in hybrid batteries.
- ADAC study.
The long-term reliability of electrified vehicles is a big unknown for thousands of drivers. While battery electric vehicles (BEVs) are generally perceived as having good battery durability, a recent large-scale analysis has confirmed what many experts suspected: plug-in hybrid (PHEV) batteries age in a fundamentally different and often faster way, with significant differences between brands and modes of use.
The study, conducted in 2025 by German automobile club ADAC in collaboration with battery diagnostics company Aviloo, analyzed real data from more than 28,000 plug-in hybrids of various makes and models over a six-year period. The result is a detailed map of the degradation of these systems, a finding of vital importance for the growing second-hand vehicle market.
- Charging and recharging cycles.
The main conclusion of the analysis is that plug-in hybrid batteries tend to lose their useful capacity more rapidly than those in electric vehicles. This difference is not due to a design flaw, but rather a matter of pure operational physics related to the size of the battery pack.
The batteries in plug-in hybrids are inherently smaller and, in order to provide functional electric range, are subjected to greater cycling stress. Over the life of the vehicle, the battery in a plug-in hybrid experiences many more “equivalent full cycles,” and each kWh of its capacity is “worked” more intensely than in a 100% electric vehicle. This intensity in the charge and discharge cycles increases chemical wear on the cells.
Added to this is thermal management. Latest-generation electric vehicles typically have sophisticated active cooling and heating systems that keep the battery within an optimal temperature range. Plug-in hybrids, especially older generations, often make do with simpler thermal management systems, exposing the internal chemistry to greater temperature fluctuations and accelerating aging.
The ADAC study not only identified the cause of degradation, but also established the expected state of health-SoH percentages based on mileage. This data becomes a valuable tool for those considering the purchase of a used plug-in hybrid.
According to measurements, the average SoH of plug-in hybrid vehicle batteries should be at the following minimum values:
- 92% after reaching 50,000 kilometers.
- 88% after reaching 100,000 kilometers.
- 84% at around 150,000 kilometers.
- 80% after exceeding the 200,000-kilometer mark.
The good news is that most of the vehicles analyzed maintain an SoH level above 80% even after traveling 200,000 km, a figure that most manufacturers guarantee.
- Usage factor.
One of the most interesting, and to some extent counterintuitive, findings relates to driver behavior. The study confirmed a strong correlation between usage patterns and battery longevity.
Paradoxically, cars that were driven more frequently in pure electric mode, also known as charge-depleting mode, showed faster degradation of the battery pack. Conversely, those that relied more on their combustion engine tended to preserve their batteries better. The reason is simple: every time electric mode is used, the battery pack undergoes a discharge cycle. The more cycles performed, the more stress is added to the battery.
Rarely used batteries, the yellow dots are concentrated in the upper range, where battery capacity is good. The wide dispersion of the points illustrates that, in addition to usage patterns, factors such as manufacturer, model, battery type, cell defects, and temperature influence battery life.
The differences between manufacturers were significant and are crucial information for users.
Mercedes-Benz plug-in hybrid models stood out for their stability, maintaining remarkably high and stable SoH levels even after exceeding 200,000 kilometers.
At the other end of the spectrum, some Mitsubishi models showed significant and early degradation, even with low mileage, although this trend subsequently stabilized.
Vehicles from the Volkswagen Group and Volvo remained in a range considered “unremarkable,” while BMW models showed considerable variation in degradation, which was directly dependent on the degree of electric use.
This study highlights that, while plug-in hybrid technology offers undeniable flexibility, it requires special consideration in terms of battery durability, which is very different from that of pure electric vehicles. For those buying a used vehicle, it will be essential to check not only the mileage, but also the charging history and, above all, the make of the vehicle.
- Implications for fleet management.
The main consequence is the loss of range and residual value of the vehicle over time.
The following measures are recommended.
- Vehicle purchase.
Before purchasing a plug-in hybrid, it is recommended to conduct a study on the battery degradation of that vehicle model. It is important to understand how the battery degrades.
As discussed in the study, there are significant differences between vehicle manufacturers.
The sources of information are studies conducted by organizations such as ADAC, the vehicle and battery manufacturers themselves, our own experience with fleet vehicles, other vehicle fleets, or Internet searches.
- Purchasing a used vehicle.
Before purchasing a used plug-in hybrid, it is important to consider the mileage, charging history, battery state of health (SoH), and, above all, the vehicle brand.
- Selling the vehicle.
As discussed in the study, some vehicle brands experience greater battery degradation, which means the residual value of the vehicle is lower and it will be more difficult to sell.
- Battery replacement.
The cost of a plug-in hybrid battery is high, and the cost per kWh/kg of a plug-in hybrid is higher than that of a 100% electric vehicle.
Plug-in hybrids are normally used in electric mode and with the internal combustion engine.
If, for example, the electric mode has a range of 60 kilometers, and over time 20% of the battery is lost, we will have lost 12 kilometers of range, leaving us with 48 kilometers of range.
It is not recommended to replace the battery of a plug-in hybrid because it has lost range. The high cost of the battery is not offset by having 10-15 kilometers more in electric mode, especially if you can also travel those kilometers with the internal combustion engine.
Slide 3. Thank you for your time.
The class has developed the degradation of plug-in hybrid batteries and the implications for fleet management, see you soon.
