Hi!
From all I've read and saw so far I personally belive it to be highly unlikely that there are still "new" and matched cells around to be build into old frames.
Just as a reminder, the 85 battery pack consists out of 7104 single cylindrical cells. 74 cells put in parallel are called a brick and there is one voltage sensor per each brick. 6 bricks form a module, 16 modules form the whole pack. So far I believe there are certain "hard" limitations imposed by the BMS depending on the voltage at the top/bottom soc but also different brick voltage during charging/discharging, add to the mix the coolant temperature etc. As often described in this forum the top level voltage per brick is 4.2V, therefore => 4.2V x 6 bricks x 16 modules = 403.2V Battery Pack max Voltage. Also the BMS protects the battery not to be discharged too deep, allegedly when at least one brick is dipping below the 3V threshold by disabling drive mode and later shutting down the whole 12V system. From personal experience: When drive mode is disabled make sure to set the suspension to the highest level, enter service- and tow-mode, also disabling the alarm is a good idea. Thus the car can actually be towed or rolled onto a trailer by winch, just saying...
I actually do believe that the BMS calculated rated/typical range could be increased @100% soc by following a certain charging behavior, yet this will not change (significantly) the actual amount of energy you can get out of your battery.
But perhaps the adviser was right and you actually got new & unused cells, initially produced and matched to form a 85 battery. How to confirm that? That is tricky on your end, some methods come to mind...
1) You could drive to a SeC and ask them to show you the onboard Diagnostic Mode, Basic tab, scroll down to the BMS section and you should look for something like this:
View attachment 776172
The above example would be from a car with f/w 2019.12.1.1 (148,438mi) and therefore with neither Brick Voltage nor Supercharging limitation. Good times, long gone.
2) Another option to gain access to the above data would be through an ODB2 dongle attached to your car and sending information via bluetooth to a paired e.g. android phone with the app "ScanMyTesla".
3) The
CFDERU-method (Charge Full Drive Empty Read Used)
a) Plan a charging session e.g. to leave next day with maximum (range charge or 100%) at xx o'clock. Add another 60 minutes to actually reach 100% soc. There are a number of cars whom will stop charging and never being able to go above e.g. 98% or 97% SOC. (*)
Hint: For the sake of your Battery: Do not let the car stand (long) with maximum / 100%. It should be of no lasting impact once in a while when you use the car right afterwards to at least 90% soc or lower.
2) Start driving. When climate allows, keep heater/hvac turned of. Plan your route to drive the battery to <10% or even better ~5% soc to arrive at a charger. If you are adventurous go even slower. Yet there were instances, when Teslas shut down with 2, 3, 4, or even 5% SOC left, rare occasions and afaik unheard with a fresh installed reman battery, but you never know.
3) When reaching your lowest SOC the trips counter "since last charging" shows an accurate number of distance driven and kWh used while driving, giving you a lean buffer of 5% at the bottom and showing you what to expect.
You want to calculate the used kWh at 0%? When charged to 100% SOC and driven down to e.g. 5% SOC, you have a delta of 95% = 0,95. Next divide the used kWh by the decimal delta and there you are with your usable Energy.
Albeit, since Tesla is "adjusting" the calculated remaining range/soc at arrival depending on the current SOC, you cannot simply charge from e.g. 37% to 82% and expect to calculate the same kWh if used from full to zero. Yet when charging next to 100% or whatever max your BMS allows and discharging to or below 5% you should be able to circumvent these "adjustments"... You want to know what I am referring to? Okay, you asked
Try the following "Experiment": During your next long range trip when arriving at a SuC with e.g. 5% remaining SOC, plug in. and choose the next charging stop, skip the remaining charging time indicator by restart routing. In the Route overview the SOC at arrival is somewhat negative, e.g. -32% at arrival. For some time now you will be able to see that the SOC will raise in 1% increments and the SOC at arrival will do exactly the same... -31, -30, -29 etc. until it reaches 5%. You will notice that the SOC at arrival will be stuck there until your actual SOC raised ~5% and only then both of them will restart to raise in parallel.
Hint: Since Corona I am charging usually once a week to 94% SOC and park then with 89/88%SOC. The "vampire" drain is rather high throughout the winter. Normally I drive on a daily basis, leaving the car to rest over night with less and less SOC until ~10% and again, leavi git overnight and charge in the morning. Different during summer, way less loss , normally I will drive down to 5%, leave it overnight and drive the next morning to the free SuC. These behavior created a well balanced battery, as I was told, by leaving the car to rest with various SOC. Some claim under a certain SOC the aging is even highly reduced.
(*) A brand new 85 Battery back in the day had no problem to charge to 100% even in a timely manner. Perhaps this is limited now by the BMS regardless the age, but I would hope that a truly brand new pack would be different.
BR Oaito.