The amount of energy a battery is capable of storing and delivering is rated in Amp-hours or Ah.
The CAC reading in a Telsa Roadster ESS Battery Pack is an internal estimate of the Roadster Battery Capacity in Calculated Amp-hour Capacity (CAC) which can be read from the ESS service screen.
As Tesla Roadsters age, this measurement becomes more important since the CAC rating reveals the health of the main battery, a barometer for battery capacity.
To gain access to this specification requires entering the holy grail level in the Tesla Roadster firmware, at one time a diagnostics menu reserved only for Service Center technicians. Please follow these steps:
First, we need to get to the hidden password protected menu.
You do so by tapping several times on an non-non-interactive area of the VDS screen—see red circle in the image on the left.
A passcode screen will pop up and you will need to enter a password of 1050 and select OK.
You will then end up on this System Diagnostics screen.
Select the ESS button, which stands for Energy Storage System, a fancy name Tesla coined for the Main Battery Pack.
On the ESS Screen, Select the SOC button.
SOC is an acronym for “State of Charge”.
This submenu is loaded with stats such as the CAC, or Calculated Amp-Hour Capacity, or recent SOC log stats, all pertaining to the Main Battery Pack.
On the ESS SOC Screen, you will now see the CAC rating.
As the Roadster battery packs age, the CAC level will decline. Another indicator of age is the mileage range in either standard or range mode (not recommended).
Here is where we are seeing the majority of current Tesla Roadster ESS Pack CAC readings.
Brand new, the CAC readings were 157 – 157, and we have seen low mileage Roadsters, with legacy packs, in the low 150’s. The new 3.0 packs currently manufactured by Tesla, typically report CAC values of 200 – 220.
We are always available either by phone, 800 658-5883 Extension 500, or email ev@gruber.com, for free tech support.
As always, our goal is to support the Roadster community. We believe in transparency, and are committed to vehicle owner education.
