I thought I would wait until one of the more dedicated/knowledgeable nerds on the Battery subforum would chime in and offer an explanation for what the OP has observed/posted. But, I just couldn’t resist. So, the short answer is your vehicle did not gain or even maintain any range during the extended period that you parked/stored your vehicle. Here is what actually happened (and the long answer):
On the date you parked/left your vehicle, the BMS (Battery Management System) in your vehicle calculated/reported what it believed was your SOC (State of Charge) and the estimated available range at that particular point in time. However, as most of us nerds know, the vehicle’s BMS system can be a little “off” in what it reports on your display screen. So, what happens is, after several hours of being inactive/asleep, the vehicle’s BMS will take some internal readings on the battery pack’s actual SOC and other measurements. Then, the BMS uses these newer measurements/readings to “recalibrate” its calculation/estimate of the SOC and available remaining range. I do not know how often Tesla vehicles perform this internal reading/calibration while parked/asleep for extended periods. Perhaps one of the true Tesla battery gurus on this forum will chime in with their thoughts. However, I do think the BMS in our vehicles will perform this internal reading/calibration several times while the vehicle is parked for an extended period of time.
So, in the OP’s case, what he/she observed was the BMS reporting a particular estimated SOC/range on the day he/she parked the vehicle… which turned out to be a little lower than the vehicle’s actual SOC and available range. In other words, the values reported by the OP’s vehicle was a little “wrong” and on the low side. But, while the OP’s vehicle was parked, the BMS performed additional readings/calibrations and then adjusted and “corrected” the estimated SOC/range accordingly. It just so happens that the adjusted values came out higher than what was previously calculated/reported on the day the vehicle was initially parked/left.
So, the above explains why the OP saw a higher SOC/range when he/she returned to the vehicle a week or so later.
The vehicle definitely did NOT gain any real SOC/range while it was parked. There should be no question/doubt that all modern day batteries will lose some energy/range while inactive or stored for any period of time. Again, the OP’s vehicle simply reported an “incorrect” value when he/she left it. In reality, his/her vehicle’s actual SOC at the day/time it was parked was likely closer to 53 or 54% (instead of the 50% that was initially reported).
By the way, I have observed a similar behavior with my vehicle. When I return from a trip and park it for the evening, it will report a particular SOC/range. Then, the next day, it will sometimes report a slightly higher SOC/range than the night before. It’s simply my vehicle’s BMS performing a recalibration and ”correcting” itself…
Hope the above explanation helps some folks sleep better at night ...
You’re welcome
@jjrandorin