There’s a lot to the GMC Hummer EV. Whether you talk about the truck’s performance metrics, off-road prowess, or its physical presence, the numbers are always staggering. Perhaps no part of the truck exemplifies this more than the battery pack, which is among the largest fitted to a production vehicle. R&T sat down with the team from Munro & Associates who recently tore down a Hummer EV battery to learn more about what makes this behemoth roll.
Munro & Associates is a manufacturing and engineering consultancy firm based in metro Detroit, which works alongside automakers to streamline production processes and maximize profits. To that end, it’s worth noting that the Hummer EV battery provided to the firm for a teardown did not come from General Motors directly.
The team’s recent video teardown of the Hummer battery pack raised some eyebrows among the EV faithful. One of the main areas drawing concern is the casing itself. Whereas most electric vehicles on sale today utilize lightweight aluminum extrusions in their battery cases, GM utilizes steel. The battery case is formed from 139 individual stamped steel components, which are then spot-welded together with some 3500 welds. Critics were quick to state they felt GM should be using aluminum in an effort to reduce mass, and that using welds is too costly. While those criticisms have validity, the team at Munro provided good reasons as to why GM might be taking the welded-steel route. Part of that decision could have a lot to do with what Ford is doing just down the street with its aluminum cases and composite battery tray covers.
“More than likely the Lightning and Mach-E were occupying a lot of the capacity for other people to do that style case,” Munro’s Kevin Harty tells R&T. “If Ford decides to go away from that strategy in the future, you might have availability for some of these composites and other things. But there is only so much capital to spread around. I think one of the reasons Rivian has smaller stampings and has done things a bit differently is because they’re not building in Detroit. They might not have access to the same capital equipment that the Big Three does, and the suppliers that support the Big Three in the Detroit Metro area.”
To that same end, utilizing stamped steel components actually gives GM some flexibility on the equipment side of the manufacturing process. The parts can be made by either a high tonnage or a low tonnage press, with the former being able to stamp a significant number of these parts at one time. Harty also noted that the case design itself is made in a copy-and-paste style, where the layout is repeated throughout. This further simplifies individual component manufacturing, even if extrusions are often a less capital-intensive undertaking.
“I wouldn’t necessarily throw shade at General Motors for using steel,” says Harty. “Given [the Hummer] is an off-road vehicle, the size of the battery, and then again, the mass begets mass. Oftentimes depending what you’re trying to do, steel has better properties, and you can kind of come in lighter in steel than you could be in aluminum. So, the thing I see with it is yeah, it is a large battery pack so it does have to encapsulate that, it’s a lot of pieces, there is a lot of welding. Whole cars are kind of built the way GM is building their battery pack.”
The sheer size of the Hummer EV’s battery has also been a natural point of contention. The truck comes equipped with a pack containing 24 modules of pouch cells, which total 246 kWh. Only 212 kWh of that battery is actually usable, but that’s still enough to give the Hummer EV one of the highest capacity ratings in the world. That battery has enough juice on board to provide the Hummer EV with 329 miles of range, which it achieves at a rate of 47 MPGe combined. For reference, Tesla’s Model X SUV gets 102 MPGe, whereas Ford’s Mach-E gets 90 MPGe combined. Part of that inefficiency comes down to the fact that the Hummer is a 9000-plus pound machine driving around on 35-inch tires, but the battery itself plays a role in that equation. The pack alone tips the scales at over 2800 pounds, or about as much as a Subaru BRZ. It also raises the question as to whether or not machines like the Hummer EV actually make sense in a world concerned with environmental impact.
“You can say that Formula 1 is wasteful, but you know over a five-year span they improved internal combustion engines from 30 percent thermal efficiency to 50 percent,” says Murno’s lead chassis systems engineer Chris Purser. “That previous 10 percent to 30 percent took 100 years. It’s a good way to get money into the area to pay for R&D and real-world testing. GMC is not trying to make a mass-market commuter than a million people are going to drive. It’s to prove out the technology and to prove to the world that the technology is robust enough to buy that $45,000 commuter and not worry that it’ll crap out in two years.”
Murno does believe there are some areas in which GM might be able to draw more profitability from the pack, though we’ll need to see other Ultium battery teardowns to know exactly what is shared between models. We shouldn’t have to wait too much longer for someone to get their hands on one of those batteries, with models like the Cadillac Lyriq and Chevrolet Equinox EV in production at this point.
“The 24-module Ultium battery pack for our battery-electric trucks is among the industry’s best in terms of the energy it provides for every kilogram it weighs and liter of volume it occupies,” a GMC spokesperson tells R&T in a statement. “It also provides concentrated stiffness low in vehicles to enable features like removable roof panels and extreme off-road capability. It was designed to house enough energy for what we know our truck customers want—up to 450 miles of range on a single charge and towing up to 10,000 lbs. The Ultium truck battery pack represents one extreme of the flexibility of our Ultium Platform, which can also efficiently provide energy for upcoming small and affordable vehicles in our lineup.”
That’s not to say that the Hummer EV’s Ultium battery system is perfect. Tesla’s 4680 pack is the most efficiently executed on the market today according to the Munro team, while other automakers have made exciting efficiency gains with lower overall cell counts than we see from GM. Limiting cell count can be an important cost-saving measure, as each kWh of capacity currently costs automakers an average of between $120 and $130, according to Harty.
“In some ways this pack kind of feels like the hardware equivalent of the software kind of ‘move fast and break things’ approach,” says Purser, referring to a longtime Silicon Valley mantra. “Just get a product out there and then see where you can nit-pick later and speed up your code. Or like just build a pack and we’ll see where we can get the cost out later.”
The GMC Hummer EV succeeds in its mission of being an outrageous centerpiece for the automaker’s electric vehicle efforts. It’s inarguably impressive to see what a vehicle of this size is capable of, even if we don’t all think these are the things we should be building. That capability is owed to the Ultium battery system, even if it’s not the most efficient or cost-effective battery design on the market. That might not matter as much to a vehicle that costs over six figures, but it will be important for GM to find savings somewhere in their EV platforms to ensure affordable offerings for the public at large.
