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Over the years we have had several discussions about how to properly prepare your battery for its battery test (supposed to be an annual thing). It seems like the European techs do things a little differently than the US techs.

Here are the directions that I believe the Euro techs follow:

Battery - Maintenance or Status Check of High Voltage Battery
Date: May 6, 2014
Order No.: SM-B-54.10/09
Group: 54
SUBJECT: MY-All, Model 451.390/391/490/491
Preparation for Performing Maintenance Service or Status Check of High-Voltage Battery

"Drive vehicle (discharge) to < 40 % SOC (see left-hand round "SOC" dial on instrument panel).
^ Leave vehicle parked for approximately 2 hours (no driving, no charging).
^ After this idle period of approximately 2 hours, connect the charging cable, and fully charge the vehicle to 100 % SOC.
^ The vehicle can then be operated normally again.”


The US techs seem to not know, not care or plain disregard the above directions.

So to satisfy my curiosity, I ran the battery test by both following the directions and again by just doing the test without paying any attention to the suggested directions. I ran the test with a 20% charge, then again with that same 20% charge after about six hours of sitting and finally the next morning at a 100% charge. The most important numbers that I look at are the reported Ah numbers for CAP max, min and mean. They were identical on all three tests as were the numbers for the 93 individual cells. I tested both of my cars below three times and the results were the same for each.

So unless someone tells me otherwise, it doesn't seem to matter what procedure you use to do the test.

Len
2014 EV Coupe 15,000 miles
2014 EV Cabriolet 5,000 miles
 

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They were identical on all three tests as were the numbers for the 93 individual cells. I tested both of my cars below three times and the results were the same for each.

So unless someone tells me otherwise, it doesn't seem to matter what procedure you use to do the test.
I believe the "test" is done by the car whenever certain conditions are met. The results of the test are recorded in the memory of the BMS (battery management system) and the BMS reports the results of the most recent test when queried by the little green box.

Assuming that is correct, it's not surprising that all the "tests" (with the little green box) report the same results. It's quite possible that it's reporting exactly the same test.

The key is getting the car/BMS to do the capacity test. Whatever the BMS needs to see in order to commence a test is all that matters. If you look at the "Last Measurement: NN days" figure on the BMS test output, that will tell you when the test was last run. If you keep getting the same test date in the past, you're reading the results of the same test.

I think in your 3 uses of the green box, you read the results of the same (one) test 3 times or maybe 2 tests. That initial test happened when you followed the discharge under 40%, let sit 2 hours, then fully charge procedure. The subsequent drain to 20% and retest at 20% read the same test results, as did the let it rest 6 hours at 20% and test. It's possible that the last full charge got you a second test.
 

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Makes sense - thanks. I knew that the battery did a self test anytime it met the conditions above. I guess the directions in the service manual are to make sure the tech pulls up current data and not something weeks or months old if the car never went below 40%.

All three tests on the cabriolet show the last test as 0 days ago. The three tests on the coupe show the last test as 14 days ago. Wonder why the coupe didn't give me a 0 days too, since I met the criteria. Might have to run it again to verify.

Len
2014 EV Coupe 15,000 miles
2014 EV Cabriolet 5,000 miles
 
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