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Friday, December 2, 2022

How Big Is The Tesla Semi-Truck Battery Pack?

Tesla delivered the first of their semi-trucks to a customer last night. The Pepsi / FritoLay company was the lucky customer. We learned a lot about the vehicle's capabilities in the presentation, but one thing we didn't learn is the size (energy capacity) of the battery pack. 

In this entry, we'll use what we know about the battery to put upper and lower bounds on the capacity and infer a likely size. If you don't want to read to the end, our current estimate for the size of the battery pack in the Tesla Semi is 914kWh usable. Read on if you'd like to know how we came to this conclusion. 

We know the cells are produced at Giga Nevada and, given the hauling use case, they are likely the high-Nickel chemistry that was developed in partnership with Panasonic. 

Tesla has said that the semi (fully loaded) has an efficiency better than 2kWh per mile. Additionally, the semi recently completed a fully loaded 500-mile drive. 

Using these two numbers gives us a 1000kWh (1GWh) capacity estimate, but there's more to the story. 

Taking a close look at the drive above, you can see that it started with 97% charge and ended with a 4% charge; so if you were doing a true 100 to zero percent trip, you'd have another 7% of capacity to use. That would be a 537-mile range, at 2kWh per mile, the upper bound for the pack size is 1,075kWh. 

As Musk often does, he gave us more info on Twitter. Specifically, he said that the current efficiency of the semi is 1.7kWh per mile. Another digit of precision would be nice, but we'll go with this for now. 

Recalculating using this number and the 500-mile trip yields an 850 kWh battery. Using the inferred 537-mile trip would use a 914kWh capacity battery pack usable.

In battery-powered electric vehicles, there's usually some reserve capacity that's locked away from the driver's use. This helps extend the battery lifespan. If we assume a 6% reserve, this adds another 55 kWhs to the pack, bringing the total pack size to 969kWh.

A 1.7kWh/mile efficiency is the energy equivalent of about 20 miles per gallon (20 MPGe while hauling a full load). For a comparison, with a full load, Diesel class 8 semi-trucks average about 6 MPG. The most efficient Diesels semis out there (the Freightliner Cascadia Evolution) gets 10 MPG on a good day. So the Tesla Semi has a fuel efficiency that's triple the average (and double the best), compared to Diesel semi-trucks.

Today, semis are primarily Diesel-powered. Electrifying semi-trucks is very important. In the US, they are only about 1% of vehicles on the roads, but they have a very outsized pollution impact; they generate about 20% of vehicle emissions and about 36% of particulate emissions. This directly has an impact on health and air quality. Semi-trucks from Tesla, Freightliner, BMW, and others will help make a cleaner world. 


  1. We also did not hear how much the cab weighs. This can be a significant factor, as it will limit the amount/type of cargo that can be carried before crossing the magical 82000lb limit.

    It does seem as if it is fairly efficient, which is cool.

    1. True, we don't (yet) know the cab weight. However, battery tech is advancing and with each generation, the cab weight we be lighter and the cargo weight will be better. When the semi production moves to 4680 cells (and to Austin), we can expect an improvement. Until then, there are still plenty of use cases for lighter cargo loads.