A study highlights the varying degree of battery degradation over time in plug-in hybrid vehicles

As is the case with fully electric vehicles, plug-in hybrid batteries lose charge capacity over time. A recent study by the German automobile club ADAC, based on data collected from nearly 28,000 vehicles with this propulsion system, reveals that the level of battery degradation in plug-in hybrid models varies substantially depending on the brand.

The analysis carried out by ADAC shows that the batteries of Mercedes-Benz plug-in hybrids tend to suffer a slow and stable level of degradation. Even after covering 200,000 kilometres, the German manufacturer’s models with this propulsion system retain on average almost 90 percent of the battery’s original capacity, regardless of how much they are used in electric mode.

BMW, for its part, shows a somewhat steeper but predictable curve. At those same 200,000 kilometres, the Bavarian manufacturer’s models that cover few kilometres in fully electric mode retain more than 90 percent of the battery’s original capacity, those with medium use hover around 85 percent, and those that try to avoid fuel consumption by driving in electric mode whenever they can retain close to 77 percent of the battery’s original capacity.

Not all plug-in hybrid batteries behave the same way

Other brands such as Volvo show a level of battery wear rated by ADAC as “normal”. Whereas Ford or Mitsubishi disappoint. The plug-in hybrid models from the North American manufacturer suffer strong degradation early in the vehicle’s life, losing up to 10 percent before the first 25,000 kilometres, while with those from the Japanese manufacturer the situation is even worse. The data collected by ADAC reveal a degradation level above 20 percent within the first 100,000 kilometres driven, exceeding 25 percent at 200,000 kilometres. In extreme cases this percentage even reaches 30 percent.

To all those drivers planning to buy a used plug-in hybrid, ADAC recommends always checking the health of the battery before completing the purchase, and offers a benchmark for what should be considered a normal level of degradation. At around 50,000 kilometres driven, battery capacity should be around 92 percent of the original, 88 percent at 100,000 kilometres, 84 percent at 150,000 km and 80 percent at 200,000.

Likewise, to extend the battery’s service life, this German automobile club advises trying to keep the charge level between 20 and 80 percent whenever possible, avoiding full discharges or frequent charges to 100 percent, and minimising the use of DC fast-charging points on models that allow it. Extreme temperatures are also a problem, so leaving the vehicle out on the street in winter or under the sun in the middle of summer also contributes to a greater level of degradation, especially if it is parked with the battery fully discharged.

In short, these are the same tips that apply to any electronic device that uses a lithium-ion battery, such as our mobile phone. It should also be pointed out that, in the case of vehicles with lithium iron phosphate (LFP) batteries, these tips do not apply one hundred percent, since the way these batteries work is different.