I think GM re-engineered the BT1 platform double-decked battery cases to resolve hard-to-seal gaps at the case corner top flanges. New Hummers now in production use the new cases and all of the Hummers w/ old leaky cases will get dealer-installed new packs.
It appears the Hummer SUT ED1 has been the low-volume production “test dummy” for a lot of the new GM e-truck design concepts going into high-volume Silverado and Denali EV trucks. We’ll probably see an order of magnitude fewer problems w/ Silverado and Denali rollouts.
