Here's An Exceedingly Nerdy Explanation of GM's Ultium Battery System

The Cadillac Lyriq is one of the first vehicles to use GM’s Ultium platform. This drivetrain system now underpins all of its current and upcoming electric vehicles, other than the outgoing Chevy Bolt EV. After driving the Lyriq and liking it very much, I was interested in the precise details of the car’s pack and the larger Ultium system. So I interviewed Jerry Beemer, who leads GM’s EV Propulsion team. If you want to know everything about this system down to the individual cells, he’s your guy. 

The Ultium platform currently consists of packs made from the same building blocks. The core of this system is the Ultium battery cell, a long and slender 103 amp-hour (Ah)  pouch utilizing a derivative of the nickel manganese cobalt (NMC) chemistry. That means a peak voltage of around 4.2V and a nominal voltage of around 3.6V. The upcoming Chevy Bolt will allegedly be on the same platform but will utilize a lithium-iron-phosphate chemistry. That means the peak cell voltage will be around 3.65V, with nominal coming in around 3.2V.

It’s unclear if these cells will take the same shape as the current Ultium cells, but Beemer told me the cell itself is not vital to the platform. In China, for instance, “We sell Lyriqs with a module-based pack like we have today, but it’s a different chemistry, a different form factor of prismatic cans in those packs” Beemer said. 

In other words, key things like the battery management system, module-centric pack construction, and other details, like how power electronics communicate with each other are what make Ultium what it is. The system is not defined by the 103Ah cell that most of GM’s North American EVs use.

Speaking of these cells, 24 are stuffed into each of the Lyriq’s modules in a 8S 3P configuration, giving a nominal module voltage of roughly 29V. Every module is wired in series to achieve the Lyriq’s 96S pack configuration. This detail belies GM’s confidence in its lower voltage architecture. A rework in module construction would be required to push the voltage higher. Because of this, vehicles carrying fewer modules than the Lyriq will likely operate at a lower voltage.

The Hummer EV utilizes the same cells and modules, however the