Evaluate EV battery capacity

[bwilson4web]

Used EVs will become more available and a buyer needs to evaluate the full charge capacity within a couple of hours:

• 100% SOC kWh ~= charge_kWh / (% SOC_1 - % SOC_2)
• % SOC_1 - beginning SOC from test charge
• % SOC_2 - ending SOC from test charge
• charge_kWh - how much charge was added

The greater the change in % SOC, the more accurate the expected 100% SOC kWh.

My test at the Toyota dealer, 2 hours, estimated the battery full capacity at ~27.0 kWh. Recently, I did a full charge test and measured 30.4 kWh which accounting for vehicle charger efficiency, ~92-95%, gives 28.0-28.5 kWh.

Bob Wilson

[Piotrsko]

Hmmm: Imho with a volt pack, storage capacity is difficult to determine quickly, need a couple of runs at various drains and recharges. You need accurate aero data for that unless you know motor specifics. You can look at system voltages after some use but that doesn't show individual cell condition voltages which is related to capacity. Couple of borderline capacity cells can be covered by a couple of efficient cells of higher than standard voltage. You could find out after a high discharge rate unless you have some method for reading and flagging individual cells realtime. some homebuilder BMS will do that on the can bus.

I cant see a dealer letting me play with a pack on the lot. Or even letting me plug in test equipment to the obd system.

[redpoint5]

The Leaf has an app called LeafSpy that can show battery capacity as a % of new, as well as voltages of individual battery banks so that one can determine how closely matched they are.

Does such a thing exist for any other makes/models? That makes determining battery health simple.

Oh, and the Leaf has "bars" in the display indicating overall battery health. These bars slowly decrease as the battery wears, and can give owners a rough idea about degradation (to within perhaps 5%).

[Piotrsko]

5 bars is 20% accuracy, 7 bars is 15%, 9 bars is 11%. Might be 5% accurate for displaying the correct bar, more so if it blinks between bars

[redpoint5]

Since you brought it up again, I Googled it.

Here's the Leaf battery health display. It's not linear, so you have to refer to this chart.