Why EV Structural Batteries Are a Bad Idea

Structural batteries in electric vehicles are planned obsolescence.

Structural batteries have been touted by many experts as a way to decrease electric vehicle weight, an application where every ounce is critical. Incorporating large masses like engines and batteries into the vehicle structure does reduce weight, but it makes it difficult or impossible to cost-effectively replace those units when they fail. If the economic and business model supports disposal of the entire vehicle, it’s a sensible weight and cost reduction strategy. But the environmental costs may be bigger than simple disposal of end-of-life EVs.

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Episode Transcript:

Electric vehicles and advanced technology—well, those two concepts go hand-in-hand. Not content with simply replacing the powerplant in conventional automotive designs, several manufacturers’ electric vehicles are attempting to reinvent the vehicle structure itself, right down to the monocoque, or what the industry calls the “body in white.” 

Electric vehicle batteries are heavy—damned heavy—and because of this weight, it’s essential to put the rest of the vehicle on a diet to maximize that most critical attribute of EV performance: range.

Light metal alloys and composite materials have a part to play, but several EV manufacturers are discussing another way to reduce weight: structural battery packs.

Colin Chapman, founder of Lotus Cars, used this technique in the early 1960s, developing Formula One cars in which the engine block and transmission case were structural members, saving weight and increasing performance. It’s a strategy that works, but in electric vehicles, I believe that structural batteries are a bad idea.

Here’s why: the battery is the weak point of any electric vehicle. As electric vehicles age, range decreases as batteries degrade with every charge/discharge cycle. Individual cells within a battery may die, and manufacturers have developed algorithms in onboard battery management systems to do a software workaround to isolate bad cells. But it’s likely that for most drivers, the end life of an electric vehicle will be determined by its battery, not by rotating electrical or mechanical parts.

A new replacement battery could potentially rejuvenate an older EV, not only saving the environmental costs of disposal and new vehicle construction, but creating a lower cost used electric vehicle product stream that would offer less affluent consumers full EV range.

And that’s not the only factor here. Battery chemistries are still in a state of flux, despite the prevalence of lithium-ion technology. A significant breakthrough in battery technology, which could come from anywhere, at any time, and the existing EV fleet could be rendered instantly obsolete.

If a new EV offers a 400-mile range, what is the trade-in value of your used model with 180-mile range?

Again, replaceable batteries would allow an existing owner to upgrade the technology and improve the utility of their existing vehicle. And replaceable batteries also allow the creation of an effective battery aftermarket, and even a remanufacturing industry.

Even lead acid car batteries, now effectively a disposable item, are actually re-buildable and for most of the 20th century it was possible to buy remanufactured, rebuilt car batteries from local businesses everywhere. A similar industry is slowly developing for rejuvenating electric vehicle batteries, although battery manufacturers often make this difficult by encapsulating the cells in a solid block of resin potting compound.

But I’m not holding my breath. American consumers in particular have been offered reliability and repairability as a selling feature and have generally rejected it. One example: the Checker Marathon. Taxi fleet operators loved them. Very few American consumers, however, bought them. 

But it would be great if someone would invent an EV equivalent to that Checker.

Written by

James Anderton

Jim Anderton is the Director of Content for ENGINEERING.com. Mr. Anderton was formerly editor of Canadian Metalworking Magazine and has contributed to a wide range of print and on-line publications, including Design Engineering, Canadian Plastics, Service Station and Garage Management, Autovision, and the National Post. He also brings prior industry experience in quality and part design for a Tier One automotive supplier.