Shocking Used PHEV Battery Health Study – Mercedes Wins, Ford Fails!
If you are in the market for a plug-in hybrid, this might be the most important article you read all year. A massive new real-world analysis has just blown the lid off used PHEV battery health, revealing a shocking disparity between automakers. While some brands like Mercedes-Benz are building batteries that last virtually forever, others—specifically Ford and Mitsubishi—are showing alarming rates of degradation that could leave used buyers with a very expensive repair bill.
The Study: 28,000 Cars Tell the Truth
All batteries die eventually. Whether it’s your iPhone or your car, losing capacity is a fact of life. But how fast they die is the billion-dollar question.
To find the answer, the ADAC (Germany’s largest auto club) teamed up with battery analytics firm Aviloo to analyze nearly 28,500 plug-in hybrids across six major brands. They measured the “State of Health” (SoH)—the percentage of original capacity the battery retains as it ages. The results were not subtle.
The Gold Standard: Mercedes-Benz
If you want durability, buy a Benz. The study found that Mercedes-Benz PHEV batteries are essentially bulletproof.
Even after racking up 124,000 miles (200,000 km), Mercedes models retained nearly 90% of their original capacity. Remarkably, this held true even for cars that were driven heavily in electric mode, suggesting Mercedes has mastered thermal management and battery chemistry better than anyone else in the segment.
The Steady Performers: VW and Volvo
Sitting comfortably in the middle are Volkswagen and Volvo. Their long-term battery health was described as “unremarkable”—in a good way.
Like Mercedes, these brands showed stable degradation curves. Even with heavy electric usage, high-mileage examples (124,000+ miles) still consistently returned a healthy SoH of over 85%. They are safe bets for used buyers.
The “It Depends”: BMW
BMW PHEVs are a mixed bag. The study found a massive variance depending on how the car was driven.
- Gas-heavy drivers: Owners who mostly used the gas engine saw excellent retention (over 90%).
- EV-heavy drivers: Owners who aggressively used the electric mode saw capacity drop to around 77% at high mileage. If you’re buying a used BMW hybrid, you need to know its history.
The Red Flags: Ford and Mitsubishi
This is where the news gets grim. The study identified Ford and Mitsubishi as the worst performers for long-term used PHEV battery health.
Ford’s Early Drop: The data for Ford was concerning. Models driven frequently in electric mode saw their battery health drop to 90% after just 15,000 miles. That is a steep initial decline compared to the German rivals.
Mitsubishi’s Heavy Wear: The Mitsubishi Outlander PHEV might be a best-seller, but its battery struggles are real.
- By 62,000 miles, many batteries had already dropped below 80% SoH.
- By 124,000 miles, that figure slumped to under 75%.
- Heavy users saw catastrophic drops to under 70%, effectively ruining the car’s electric range.
Expert Analysis: Why Do Some Batteries Fail Faster?
As a journalist, these findings reinforce a critical truth: PHEV batteries live a hard life. Unlike full EV batteries, which are massive and cycled slowly, PHEV batteries are tiny. They get drained to 0% and charged to 100% constantly—often multiple times a day.
This “deep cycling” is brutal on chemistry. Mercedes and Volvo seem to have solved this with robust “buffers” (never letting the battery truly hit 0% or 100%) and superior liquid cooling. Mitsubishi and Ford, however, appear to be pushing their smaller packs too hard, leading to rapid chemical wear.
Conclusion
This ADAC study is a wake-up call. If you are shopping for a used PHEV battery health should be your number one priority.
- The Safe Bet: A high-mileage Mercedes or Volvo is likely still fresh.
- The Risk: A cheap, high-mileage Mitsubishi Outlander PHEV might be cheap for a reason—its battery could be on its last legs.
Before you sign the paperwork on any used hybrid, get a battery health certificate. It could save you thousands.
What do you think? Does this change your mind about buying a used Ford or Mitsubishi hybrid? Share your thoughts below!
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