It turns out the Chevrolet Bolt EV battery pack is simpler to assemble than that of the Tesla Model 3, while the Tesla pack is more energy dense by weight.

We had an excellent video here recently on InsideEVs: “Watch Chevy Bolt Battery Reassembly." I was impressed with the ease that the Bolt EV battery pack went together. John Kelly was very thorough, even measuring the weight of two of the Bolt EV modules so we can compare those with Tesla’s battery weight as well.

WATCH CHEVY BOLT BATTERY REASSEMBLY PROCESS – 2-HOUR VIDEO

Conclusion:

GM’s pack is simpler to assemble in this author’s opinion. However, as expected, Tesla has the edge in the energy density department.

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First, a little background on how these two packs cool their cells. Tesla’s method involves running a ribbon-shaped cooling tube between the cells. They have kept this technique since the Model S and are still using it in Model 3.
Bolt battery Slide1 (1)


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Tesla has attempted to automate the assembly of the Model 3 battery pack and, unlike Model S, they are now attaching the individual cells to the cooling ribbon. This procedure is described in more detail in our article: Tesla battery pack modules made like a machine gun. It also appears likely that Tesla is attaching the cells to the cooling ribbon with glue.

Obviously, the whole process is difficult as Tesla has twice delayed the promised “5,000 Model 3’s per week” production bogey.

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The Bolt EV pack is much simpler. The individual prismatic cells simply sit on a cooling plate with a thermal mat between the cells and the plate.

Below is a great screenshot from the video showing the plate.

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Next is a screenshot of Professor Kelly lowering section 5 modules in place.

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Pretty simple and easy to assemble.


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.…and another screenshot showing the cooling plate.

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Energy Density

At the 41:57 mark in the video we have a screenshot (below) of Professor Kelly weighing modules 1 and 10 just prior to setting them on the cooling plate. We must subtract the weight of the holding fixture to get the total weight of modules 1 and 10.

Bolt battery Slide7

The Bolt EV has 10 modules: 8 with 30 cells each and 2 with 24 cells. Module 1 and 10 are the bigger modules with 30 cells. We also find 57 kWh of usable energy in the Bolt EV pack thanks to some sleuthing by fellow engineer Jeff Nisewanger in “ Jaguar and Chevy have LG in common.” This gives us 5.95 kWh for one big Bolt EV module, which results in a module energy density of 11.9 #/kWh.

Tesla battery module weights are based on weights published in HSR Motors online catalog (aka Jason Hughes). Usable energy per Jason Hughes is 98.4 kWh for the P100D pack. There are 16 modules in that pack, so we can get the energy density of 1 module of 10.7#/kWh. Energy density of Tesla Model 3 cells assumed equal to P100D cells. See “Tesla Model 3 2170 cells=same energy desity as P100D 18650 cells”

Therefore, Tesla’s module is more energy dense by weight than the Bolt EV module. Not a surprising finding.

Bolt battery Slide8

However, there is one caveat to all this. We have not included the weight of the case in our calculations and Tesla’s case may be heavier than the Bolt EV case. Why? Because Tesla’s battery chemistry is much more flammable than GM’s and it requires more armor to deflect foreign objects.

So, Tesla may not have as big an edge as these numbers indicate if we were to include the cases in the calculations.