After being away from my Tesla for 28 days, I thought I would check on amount of energy my car was using just to keep the battery at a 50% charge. The amount of energy used for a whole month just to run the instrument cluster was a whopping 77kWh. In other terms, the energy was almost a complete charge of the battery or a vampire drain of 2.75kWh per day.
In firmware 4.5, the Model S processors that run the instrument cluster and touchscreen do not turn off. This design allows for immediate response when the driver returns to the vehicle. Unfortunately this design also uses a significant amount of electricity. Tesla plans to introduce a setting in the next firmware to control the background electronics while the car is not in use – a sleep mode – that will reduce this vampire energy consumption.
Some owners have experienced this vampire drain as loss of range as they have left their cars unplugged for a period of time. In my experience, I left the car plugged in at a 50% charge for 30 days, but I can through my utility clearly look at the kWh my car used while I was gone.
The Model S in the current firmware refreshes the battery every other day. For the 30 day period, half of the graphs look like the graph below where I have a constant house vampire load of less than .1kWh, and some solar power generation during the middle of the day.
The days the Model S requested power at 10:00pm, I consistently had the following style of graph with a spike between 10:00pm and 10:45. On the graph I can extract the three data points for the time ranges of 10:00-10:14, 10:15-10:29, and 10:30-10:45.
I realize there is a tiny vampire drain from my house at the same time, but since it is less than .1kWh, I did not include that data and the vampire drain is very marginally smaller than this data.
The following data is the actual raw numbers:
At 2.75kWh per day, that is 1,004kWh per year for every Model S on the road, or equivalent to approximately 12 full charges of electricity that should propel the Model S comfortably 225 miles, or 2,700 miles of driving.
This data is consistent with other Model S drivers on firmware 4.5. Tesla representatives have reported that changes to the firmware are coming this year addressing this issue.
As an environmentalist, that data number is very significant on a yearly basis.