See the instructions on this page
VMS Log Parser for Tesla Roadster
And here are the instructions from Tesla about how to download the Roadster log file:
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How to download the log file to a USB flash drive:
- Use a USB flash drive that is 4GB or smaller.
- Ensure the key is turned OFF and the vehicle is not charging.
- Create a top-level folder on the flash drive called "VehicleLogs" (case-sensitive). This naming convention is very important.
- Insert the flash drive into the vehicle's USB port (on the center console). The Touch Screen displays an alert asking you not to remove the memory stick and providing status of the transfer. If the Touch Screen goes to "sleep," tap the screen to "wake it up." The process takes from 10-15 minutes.
- When the alert is no longer displayed, remove the flash drive.
The log file will be located on your flash drive in VehicleLogs/VIN/YYYYMMDDHHMMSS.tar (where VIN is your Vehicle Identifi cation Number).
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Use the VMS parser program you downloaded from
VMS Log Parser for Tesla Roadster and follow the directions at the bottom of that page to extract the data from the Roadster log file. It's a command line program, which means it operates quite differently compared to the software the general public uses on their Macs and Windows.
The CAC value is displayed once your extract the log file data using VMS parser. Unfortunately, there is no simpler way to get the CAC, as far as I know. Keep in mind that Tesla did not design the Roadster to make data like the CAC readily available to the owner. But it is important information when you are trying to understand the state of your battery.