Battery Pack That Makes the GMC Hummer EV Tick Is an Abomination, Teardown Reveals

When GMC Hummer was launched, we were shocked to learn that its battery pack weighs as much as a compact car such as the Honda Civic. After the Munro Live team tore it down, it became clear that the Ultium battery pack was an abomination, and GM could never make it cost-effectively.
The housing of the GMC Hummer EV battery pack 11 photos
Photo: Munro Live via YouTube | Edited
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The GMC Hummer EV has the biggest battery pack of all EVs on the market today, with a nominal capacity of 246.8 kWh. GM made some clever engineering choices when designing the battery. One of the more interesting ones is how it stacked two 400-volt battery packs to enable 400-volt and 800-volt charging. The two packs are connected in parallel if the truck is hooked to a 400-volt charging station. When the station delivers 800 volts, the two packs are connected in series, so the GMC Hummer EV doesn't need a DC-DC converter to handle either voltage.

Still, GM also made some stupid choices in other areas, and the recent teardown by Munro Live reveals that the Ultium pack is not so cleverly designed after all. Right from the start, engineers Antonio DiNunno and Julian Aytes brought up the challenges posed by the 2,818-lb (1,278-kg) battery pack, which is as heavy as an entire compact car such as the Honda Civic. And this is not because of the 24 modules in the pack but because the battery housing is carelessly designed.

One of the reasons why the pack is so heavy is because its housing is made entirely of stamped steel. This is unusual because most battery packs feature some aluminum parts to bring the mass down. It's as if General Motors really struggled to honor Hummer's legacy by designing the heaviest battery pack for the heaviest EV possible. This goes against the EV wisdom, which dictates lowering mass as much as possible to minimize rolling resistance and improve efficiency.

The battery pack is not only heavy but also unnecessarily complicated, with the enclosure comprising 139 stamped components that are then welded together. The Munro Live team estimates over 3,500 welds on the housing alone, adding to the manufacturing costs. The battery pack also uses a complicated power distribution unit packaged in a very tight space.

Going down to the module level, the team reveals that the GMC Hummer EV uses 24 battery cells in each module. They are separated by mica layers so that a thermal runaway event in one of the cells would not spread to the adjacent cells. Each cell has a capacity of 103 Ah, which is much more than even Tesla's 4680 cells. If one or more cells misbehave, the GMC Hummer EV will lose quite a bit of battery capacity.

The key takeaway from this teardown is that GM is likely losing a lot of money on the GMC Hummer. It will continue to do so if it doesn't change the fundamentals of the Ultium battery pack. Maybe this is why GM is throttling Hummer EV production and only delivered two trucks in the first quarter. The situation appears to be better with the Cadillac Lyriq, so we're curious to see what the battery pack on that one looks like.

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About the author: Cristian Agatie
Cristian Agatie profile photo

After his childhood dream of becoming a "tractor operator" didn't pan out, Cristian turned to journalism, first in print and later moving to online media. His top interests are electric vehicles and new energy solutions.
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