Curious charging calculations

[B_Wagon136]

Just had a big overnight charge session from 10% to 80%.

I have a Gen 1 Dual Max Performance. Yes it is winter but I live in SoCal and that is not a factor at these temps.

The vehicle consumed 85 kWh to gain 70% charge (from 10 to 80%). If 85 kWh constitutes 70% of my battery capacity that meant that 100% capacity is only 121 kWh, not the stated 141 kWh for Gen 1 Max. (Rivian roamer currently shows 143.9 usable kWh in my battery pack).

The mileage range also increased from 40mi at 10% to 325mi at 80%. That’s 285 miles of range for 85 kWh, equating to 3.35 mi/kWh. Ain’t nobody getting that kind of efficiency.

So, uh, what gives?

And for the sake of clarity, the 85 kWh consumption im referencing is what was received by the battery itself, not the extraneous amounts that went to other systems (pic attached)

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[JacobAZ]

Short answer is the amount of electricity provided to charge and SOC for the battery are calculated differently. Electricity flowing through a wire can be accurately measured (volts and amps). On the other hand, a battery SOC can't directly be measured, its calculated. The 87.2 kwh is an exact measurement either of what the EVSE is delivering to the Rivian onboard inverter or the output from the inverter, not sure which Rivian measures (there are small efficiency losses). SOC is calculated based upon the voltage coming out of the battery. As a battery drains the voltage drops (its the amps which varies depending upon the power needed). In lithium batteries from about 10% SOC to about 90% the voltage drop is very small. So, think of it as the BMS is measuring the voltage out of the battery against a table of matching voltage to SOC. However, other factors affect the voltage including temperature (even small variations), cell imbalance, and battery degradation. The BMS does its best to factor all these things in and come up with a SOC. I hope this helps