How General Motors puts batteries through their paces

WARREN, Mich—General Motors' Global Battery Systems Lab is an outwardly nondescript precinct within the company's square-mile technical center in Warren, tucked into the Estes Engineering Center. But the lab is squarely on the front lines of GM's electric-car revolution.

Even after entering the Walmart-size facility, which has been expanded several times to 100,000 square feet over a decade of existence, its purpose isn't immediately apparent. A casual observer might think the rows of huge metal boxes could be baking Twinkies or mixing pharmaceuticals.

Instead, inside these stout cabinets, extreme energies are clashing, and atomic-level violence is escalating as GM tests the capabilities and safety of battery cells and packs for its all-electric vehicles and hybrids, and those of its competitors.

The lab has three new 600 kilowatt battery cyclers, for instance, and soon will have 16 more—at a cost of more than a half-million dollars each, including infrastructure—to conduct tests on batteries. With the rest of the lab battery cyclers, they will use more juice at times than it takes to power all the households in Warren, a Detroit suburb of more than 135,000 people.

"We're trying to wear out the batteries, which are going to have to take hammering on the accelerator, or maybe hauling a load up Pikes Peak," said Douglas Drauch, the lab's lead engineer.

Other cabinets are environmental chambers that mimic climate and weather extremes. "We can set things up for deserts, rain forests or Nome, Alaska," Drauch said. "We can set temperatures for as low as minus 90 degrees Fahrenheit, which you actually find only in some town in Siberia."

And in one room, a giant, $2 million "shaker" simulates how rough-and-tumble journeys on various surfaces will affect battery systems over time. An $8.5-million shaker soon will be installed, meant to handle the larger battery packs in future EVs.

GM said it has the largest battery-testing lab of any automaker globally. Nearly all such testing now can be done under this single roof, reducing cost and development time.

Durability and safety

The lab's crucial overall goal is to ensure not only performance but also durability and safety of GM's battery systems, because the company is promising that its battery systems will last for the life of its new EVs and hybrids.

The auto maker said it invested $28 million in the lab last year for new test chambers and advanced equipment to "help us accelerate our next-generation battery architecture."

The lab takes the results of mathematical simulations and compares them with physical testing of battery cells, packs and systems for performance in conditions such as extreme vibration, wild temperature ranges, human abuse, weird driving situations—and accidents.

"Basically, the lab is there to confirm the models produced by simulation," said Tim Grewe, GM's head of global electrification and battery systems. "It's impossible to test every situation under every scenario the way that people will use these cars."

A major emphasis is determining how performance and safety parameters change when putting cells into packs, and packs into vehicles—such as in the Chevrolet Bolt, which contains 288 cells. "There are going to be nuances in performance when you use that many cells in series and parallels," Grewe said.

"When you test an individual cell," he said, "there's a certain assumption about its environment. But when you put that into a battery pack there will be some temperature differences, some dynamic impedance" and so on.

Particulars of powertrain performance must be tested. Cold starts are an obvious one.

"Drivers think they'll always have enough power available to start their car," Drauch said. "But chemical reactions in batteries slow down in the cold, so we need to manage thermally what's going on."

Pack practice

The lab also has to figure out how GM battery systems handle, for instance, the dynamics of a tire instantly regaining traction on dry pavement after spinning on ice. With a conventional automatic transmission, the clutch would slip and absorb the energy.

"But in an electric car, there is no clutch, and it's a vicious transience, so all that energy will translate immediately into the battery pack," Grewe said. "The wheel inertia plus the motor inertia turns into electrical energy, and the pack has to be able to surge and suck it up. So we practice it at the pack level in the lab to make sure we don't miss it in a designer simulation. The worst thing in the world would be to break a half-shaft in development."

Other key tasks in the lab are to simulate the effects of time on battery durability and safety and to conduct "competitive analysis" of rivals' batteries.

The lab also is trying to optimize recycling of battery systems once their days powering vehicles are numbered. "We want to get all the usable value out of them before recycling," said Peter Karlson, battery-lifecycle manager.

It's not too much of a stretch to compare GM's work in its battery lab to fail-proofing a space flight. "It's an Apollo-level challenge," Grewe said. "We actually call some of these projects moon shots. We just have to avoid the fate of Apollo 13."