[RedDevil]

Originally Posted by JSH

Using interchangeable modules makes battery packs cheaper not more expensive. Let me explain:

Say a company has 3 different battery packs. They could make 3 individual lines with one dedicated to each pack. The assembly line itself would be less expensive but also very inefficient. The problem is volume and changes in volume. Say the volume are:

Pack 1 - 25,000
Pack 2 - 70,000
Pack 3 - 5,000

The assembly lines for the low volume packs likely wouldn't even run 1 shift. The company could design the low volume lines to be slower and use less people but that is very risky. What if the volume changes or wasn't what the sales guy projected. What if pack 1 actually sells 10,000 and pack 3 15,000. Now the slow line can't keep up and you are running weekends paying time and a half and double time. With dedicated lines you are always as risk that the volume is lower than expected or higher than expected. In either case it destroys efficiency and adds cost. If you aren't running 80% capacity you are throwing away money.

With flexible lines a company could make 2 lines with capacity for 60,000 packs each. As the product mix changes the blend on the line seamlessly changes. Each line is a bit more expensive but fewer lines are needed because each is run near capacity.

This is what pretty much every automaker does with their assembly lines. They make flexible lines that can run multiple vehicles on the same line. They don't batch vehicles they build them as needed. The Honda plant in Alabama makes the Ridgeline truck, Pilot CUV, and Odyssey van. They don't run trucks, then switch to vans, then switch to CUVs. You'll see something like Ridgeline, CUV, Odyssey, Odyssey, CUV, Ridgeline....

Established auto manufacturers are doing the same thing with batteries. They are using modules and assembling packs on flexible lines. They are doing this because flexible assembly, just in time, and just in sequence is second nature. They have been doing it for decades.

Then there is the service side of things. A battery pack that is bolted together and made up of modules is repairable. A tech can open it up, find the wire or module that is bad, and then replace it. Tesla's glued together battery pack is not serviceable. If it fails then Tesla or the customer has to shell out $10,000 for a complete replacement pack. (Tesla's cost not dealer cost to the customer)

But we already established that Tesla runs multiple lines producing the same pack. Any modularity is completely redundant.
There is no recent Tesla battery pack type with only a 5,000 unit run.

Also, Tesla does not make their packs serviceable for a reason.
They make them as reliable as possible, and indeed they seldom fail.
If more than 90% of packs survive the expected life of the car then it would be a bad idea to add 10% to the cost of a battery to make them serviceable.
Just changing them out for a new pack would be both cheaper and more reliable.