Tessie battery health

[tarantula]

I tried Tessie for 2 weeks. It claims my battery degradation is 12-15%. before hitting 10,000 miles. I have a feeling its battery health is more of a wild guess than a reliable metric.

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[CyberGus]

The battery state shown by Tessie is what the BMS reports. The calibration can drift over time, so try this:

- drive to low SoC (<10%)
- let it sleep (wait ~1 hr)
- charge to 100%

That should let the BMS recalibrate more accurately.

 

[tarantula]

The battery state shown by Tessie is what the BMS reports. The calibration can drift over time, so try this:

- drive to low SoC (<10%)
- let it sleep (wait ~1 hr)
- charge to 100%

That should let the BMS recalibrate more accurately.

I am not keeping the subscription. While you are right, the point that the battery health presented to the customer is inaccurate, I am afraid, stands.

 

[CyberGus]

This is my capacity over time:

It was drifting down because I was doing small charges around 50%. The large jump upward was when I took a road trip and charged to 100% overnight.

The BMS cannot make an accurate estimate on the 0-100% capacity without getting close to those values, and will be a little off no matter what tool is used to report it.

 

[James Cole]

I

This is my capacity over time:

It was drifting down because I was doing small charges around 50%. The large jump upward was when I took a road trip and charged to 100% overnight.

The BMS cannot make an accurate estimate on the 0-100% capacity without getting close to those values, and will be a little off no matter what tool is used to report it.

The question is, is the full range still usable even if you dont recalibrate?

 

[CyberGus]

The question is, is the full range still usable even if you dont recalibrate?

Good question.

The available range is estimated based on the current battery state; theoretically, the 0% shutdown point is based on the actual measured voltage.

Soooo, you might have more range than is reported, but do you really want to FA and FO?

 

[HaulingAss]

It was drifting down because I was doing small charges around 50%. The large jump upward was when I took a road trip and charged to 100% overnight.

The BMS cannot make an accurate estimate on the 0-100% capacity without getting close to those values, and will be a little off no matter what tool is used to report it.

Exactly! If the (mostly) full range of the battery is not used, there is no accurate method to determine the actual current state of charge accurately. Tesla uses very accurate methods and software calibrations to measure energy in and out of the battery in order to estimate the current state of charge at all times, but it will drift over longer time periods without having upper and lower calibrations to account for drifting accuracy over time.

If the vehicle has lived a month or more between 50-70% SOC, and then you drive it until it reads zero range left, you will probably have a nice buffer left but there is no guarantee of that because the whole reason for the buffer is to account for the fact that the computer "knows" that it doesn't know what the exact state of charge actually is (it's actually a range). Depending upon which side of that range you are on, there could be fewer than 5 miles of range left. Or, there could be 40 miles of range left.

If your battery has been taken up and down the SOC scale recently, you probably have a nice 20 miles of range left after hitting empty. If the battery has been stagnant in the middle of the range for a month, it's anyone's guess, there is no good way to tell. Of course this only matters if you need to drive past "0 miles of range left". I never need to do that (knock on wood).

 

[CyberGus]

Side note: Performing a deep discharge and then a full charge is not just about BMS calibration, it also realigns voltages across cells.

The voltage of each individual cell cannot be measured. The cells are arranged in strings of 80-something in series to get the desired 400V, and then those strings are connected in parallel. Only the voltage of a string can be measured, which is calculated as an average of all those cells.

The cells, however, do not all charge/discharge at the exact same rate. Over time, there will be a slight variance between each cell, and thus the calculated average will be less accurate. By charging to 100%, the cells should all return to their peak voltage, making the average voltage consistent.

 

[dkremm]

My stats. Charging to 80% when battery hits around 30-20ish %. Few trips, not a lot supercharging.

 

[BeFamousVideo]

My stats. Charging to 80% when battery hits around 30-20ish %. Few trips, not a lot supercharging.

Is your graph from the Tessie app? What is your odometer reading?

 

[Jager]

I am not keeping the subscription. While you are right, the point that the battery health presented to the customer is inaccurate, I am afraid, stands.

LOL.

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