It seems like you can't swing a dead battery without hitting a mild hybrid vehicle (MHEV) these days. The premise is appealing – get moderate gains in fuel efficiency and performance, provide more seamless stop-start capability, and avoid having to develop a more complicated setup with a separate charging process. Just slap in an extra 48-volt battery and hook up an electric motor to a belt drive or between the engine and transmission, and you've got yourself a mild hybrid.
Some automakers will tune the system for performance, while others will aim for better economy. Take the BMW X3 M40i, for instance. Car and Driver achieved a 4.4-second 0-60 in the non-MHEV 2021 version, then ran 4.1 seconds to 60 in the 2022 MHEV model. For 2025, the M40i has gained even more power and become the M50, but the fourth-generation BMW X3 is also really weird looking, so you'll have to decide how much the extra horsepower is worth.
The 2010 Chevrolet Malibu, on the other hand, implemented an MHEV system to boost mileage. Non-hybrid Malibus were EPA rated at 22 mpg city and 33 mpg highway while the hybrids got 26 mpg in the city and 34 mpg on the highway. Also, MHEVs aren't nearly as complex as PHEVs or HEVs, and the batteries are much cheaper to replace.
However, while MHEV batteries might not be as large and pricy as those of an electric vehicle (EV), plug-in hybrid (PHEV), or a standard hybrid (HEV), they remain more expensive and space-consuming than the nothing in pure internal-combustion engine vehicles. The average replacement price for an MHEV battery currently hovers around $1,500.
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Of course, $1,500 is an average. To find that number, we looked at prices for 10 MHEV batteries currently for sale in the USA.
Audi offers a battery for the A8, S7, RS7, Q8, SQ8, RS Q8 and more for $2,092.86, while the powerplant for the Audi A3 costs $793.34. A battery for a BMW M340i is $1,262.22, the battery for the BMW M440i is $1,161.25, and the battery for the BMW 740i is $1,596.73. You can get a battery for the Jaguar F-Pace MHEV for $1,262.37, the Mazda CX-70 is powered by a unit that costs $1,980.05, the Mercedes C-Class battery is $2,116.20, the Range Rover Velar's battery costs $1,295.26, and a replacement for the Volvo XC60 mild-hybrid system is $1,159.32.
Of course, if your MHEV is still under the factory warranty, then you don't have to worry about the cost of your mild hybrid battery at all. Although if your car's warranty runs out or is voided, the cost of that battery will suddenly become quite relevant. If you are hoping to keep your car for more than a decade, you'll also face the prospect of the battery being out of production.
This brings us to the issue of preservation. The Corvette E-Ray — which makes 655 hp, drives all four wheels, and out-accelerates the Z06 – was called a mild hybrid by Road & Track, so let's go with it for the sake of discussion. While warranty info is easy to come by for the Corvette E-Ray, the price of a battery is not. That warranty for the E-Ray's 1.9 kWh battery pack is the same as other mild hybrids at eight years or 100,000 miles, but will owners be able to source a battery in nine years?
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Mild hybrids have been around for a while. In fact, the first hybrid for sale in the U.S. — the Honda Insight — was what we would now call a mild hybrid. Car and Driver says that Toyota marketing coined the phrase to deride the Honda Insight and differentiate it from the way more complex Prius. However, the reason we bring up the Insight is not to incite an argument about hybrid terminology — it's that the Insight will give us insight as we keep future repairability in sight.
The first-generation Honda Insight was sold from 1999 to 2006 before it was discontinued and redesigned for 2009. Then it died again in 2014, was resurrected in 2018, and finally, the Honda Insight was dead again in 2022. Wouldn't you know it, Honda doesn't make batteries for those original Insights anymore. At least you can buy a third-party battery from Best Hybrid Batteries for $1,749.
Today's high-tech is tomorrow's obsolete. Automakers already cut off older models with 3G modems from subscription services because, well, 3G networks don't exist anymore. There's also no legal requirement for manufacturers to keep making parts or updates for long-dead cars, either. If future you is lucky, a company like Best Hybrid Batteries will make a replacement MHEV battery pack you can order. Otherwise, you'll have to find a shop that can recondition hybrid batteries. So, you now know that a new mild hybrid battery can cost you around $1,500 in 2025 — but perhaps the real question is what it will cost you in 2035.
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