Looking at some battery data

This first chart shows the minimum, maximum voltages and current into and out of the traction battery:

The interesting parts are the segments where the current remains constant such as 6:39:30 to 6:41:00. But there are several shorter flat discharge segments.

In this chart I selected the records where there was less than 0.5 A difference between adjacent values:

This gives us four distinct segments where the current was effectively constant. Then I combined these samples into the next chart.

The above samples were sorted in descending average of the minimum and maximum module-pair voltages:

The 3 A. samples occurred during the first part of the trip. This corresponded with the windshield wipers and possibly the traction battery fan being on. I'd parked the car where the afternoon sun was beating down on the trunk. The remaining 2 A samples seem to generate a discharge curve similar to that of NiMH battery discharge.

Taking out the 3 A samples, we get this curve:

What this suggests is we may be able to use an extended version of this technique to measure the amount of energy in a traction battery and calculate the Ahr capacity. The bad news is it probably doesn't tell us much about how long the traction battery is going to last.

Bob Wilson