Can anybody help me check the math on the following,
Considering buying a nicely spec'ed RWD 2015 S 85, but wonder weather the battery was abused or not,
- Car run 129,000 kms (80,000mi) since 2015
- In showroom currently showing 32% residual on battery
- With 282w/km (454w/mi) , the car suggests 82km (51mi) more on this battery
- This would be 82/32% = 256km (159) on a full charge
- 256 x 282 = 72,262kW for a full battery
- With a more typical 202w/km (326w/mi) this would give a range of 329 kms (204mi)
- An with the spec of 161w/km this would be 448 kms (278mi)
If this is the correct way of calculating, the car would have lost over 10% of its spec'ed range and battery capacity.
Can somebody verify, and would this mean this is a bad car?
The cars display of range may not reveal significant battery degradation. (My 90D displays a nearly new full charge range even though the usable capacity of the battery is only about 72 kwh and the real range is only about 70% of the displayed range).
The cars display of wh/mile (or wh/km) tells you about the previous owner. Not much about the car or battery.
Your 256 x 282 = 72 kwh of battery capacity calculation is not useful because it assumes that the cars display of remaining range is accurate. (It could be way off).
I don't think that any of the information that you have there tells you about the condition of the battery.
First, even when new these batteries have a usable capacity around 90% of their nominal capacity. Due to battery management features which preserve the battery. Specifically, the full charge voltage is kept a little low to preserve the battery life. And the battery is never allowed to fully discharge as this can ruin the battery immediately.
But all is not lost. You can discover the true usable capacity of the battery and the true range. It is a bit of a process. The easiest way is if the car has been driven a good distance since it was last charged. And the owner can tell you what the charge limit was when the car was last charged. That is, what battery percent, or what displayed range was the battery charged up to most recently? Assuming that the car has not been sitting around for many days, you then look at the trip computer under "Since Last Charge" and note the "Distance" miles (km) driven since last charge, and the "Total Energy" kwh used since last charge. You then use those values to calculate real range and/or usable battery capacity. In the example that you gave, the car has a charge state of 32%. If the car was previously charged to, say, 80% then the km driven and kwh used came from 48% of the battery (80-32). You divide the km driven, or the kwh used, by 0.48 and results are the km and kwh obtained from a 100% charge.
If you cannot find out about the charge state at the last charge, then you (or the owner) need to take the car on a little trip to obtain these values.
About half way down this page is what the Trips display looks like;
Tesla Model S Web Browser | Agassi TESLA
