The owner’s manual says a good Tesla Model S long term parking strategy is to expect to lose about 1% of range for every day the car is parked without being recharged.
“Even when Model S is not being driven, its Battery discharges very slowly to power the onboard electronics. On average, the Battery discharges at a rate of 1% per day. Situations can arise in which you must leave Model S unplugged for an extended period of time (for example, at an airport when traveling). In these situations, keep the 1% in mind to ensure that you leave the Battery with a sufficient charge level. For example, over a two week period (14 days), the Battery discharges by approximately 14%.”
You can minimize range loss by remembering to select the Energy Saving mode from your Power Management menu before leaving the car. But even if you do, frequent Teslarati blogger Rob M has found that range loss can be quite a bit higher than what the manual suggests. On a recent trip, his Model S showed 71% range remaining when he left the car in an airport parking lot but only 65% when he returned less than 3 days later. That’s a daily loss of 2.3%, according to his calculations.
Rob acknowledges that the weather was cold during his trip – about 16 degrees F – and he thinks that had an effect on how much power the battery lost while he was away. He suggests Model S owners figure on a range loss of 3% a day to be on the safe side.
There are reports of owners who parked their cars with less than half the normal range available and came back after a long trip to find the battery in their car completely drained. On the other hand, other Model S drivers have left their cars at the airport for extended periods and found range loss was less than the 1% figure the company says to expect.
The lesson seems to be that range loss is greater in cold weather than in warm, so make your calculations based on local conditions and leave a margin of error in your computations. For longer periods of non-use, make sure your car is as close to fully charged as possible before you park it.