When the GMC Hummer was launched, we were shocked to learn that its battery pack weighs the same as a small car like 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 GMC Hummer EV has the largest battery pack of any EV on the market today, with a typical capacity of 246.8 kWh. GM made some smart engineering decisions when designing the battery. One of the most interesting is how it installed two 400-volt battery packs to enable 400-volt and 800-volt charging. The two packs are connected in parallel if the truck is connected to a 400-volt charging station. When the outlet provides 800 volts, the two packs are connected in series, hence the GMC Hummer. IV you don’t need a DC-DC converter to handle any voltage.
Still, GM also made some stupid choices in other areas, and the recent demolition of Munro Live shows that the Ultium package is not so smartly designed. From the start, engineers Antonio DiNunno and Julian Aytes brought up the challenges posed by a 2,818-lb (1,278-kg) battery pack, which is as heavy as an entire compact car like the Honda Civic. And this is not because of the 24 modules in the pack but because the battery housing is carefully designed.
One of the reasons why the pack is heavy is because its housing is made entirely of stamped steel. This is unusual because most battery packs feature some aluminum parts to reduce bulk. It’s as if General Motors went out of their way to honor Hummer’s legacy by designing the heaviest battery pack for the heaviest EV possible. This goes against the wisdom of EV, which dictates reducing weight as much as possible to reduce rolling resistance and improve efficiency.
The battery pack is not only heavy but also unreasonably stiff, and the enclosure consists of 139 stamped components that snap together. The Munro Live team estimates more than 3,500 welds on the house alone, adding to manufacturing costs. The battery pack also uses a power distribution unit placed in a very tight space.
Breaking down to the module level, the team reveals that the GMC Hummer EV uses 24 battery cells in each module. They are separated by layers of mica so that a heat runaway event in one of the cells does not spread to the adjacent cells. Each cell has a capacity of 103 Ah, which is more than 4680 Tesla cells. If one or more cells malfunction, the GMC Hummer EV will lose some battery capacity.
The main takeaway from this debacle is that GM could lose a lot of money on the GMC Hummer. It will continue to do so if it does not change the fundamentals of the Ultium battery pack. This is probably why GM is reducing production of the Hummer EV and delivered only two trucks in the first quarter. Things seem to be going well for the Cadillac Lyriq, so we’re curious to see what the battery pack on that one looks like.