Testing my Battery Pack

So I have been getting the "Replace my battery pack" code recently. Car is close to 124000 miles. (2014 yr).

Decided today to remove the battery pack from the car and charge it up this morning with a Grid Charger to about 164V.

After letting it rest until 6pm this afternoon I then measured all 20 cells.

Module 1 8.03
Module 2 8.01
Module 3 8
Module 4 7.99
Module 5 7.99
Module 6 7.98
Module 7 7.98
Module 8 7.98
Module 9 7.99
Module 10 8.02
Module 11 8
Module 12 8.01
Module 13 8.01
Module 14 8
Module 15 7.98
Module 16 7.98
Module 17 7.99
Module 18 8
Module 19 8.01
Module 20 8.02

I then hooked up a 240V 100W bulb to the pack and measured the voltage every hour until 9pm. I decided to stop after Module 13 showed 5.76V. Here are the voltages after 3hrs.

1 - 7.28
2 - 7.26
3 - 7.25
4- 7.22
5- 7.21
6 - 7.19
7 - 7.18
8 - 7.15
9 - 7.01
10 - 6.79
11 - 6.94
12 - 6.88
13 - 5.76
14 - 6.91
15 - 7.08
16 - 7.14
17 - 7.21
18 - 7.21
19 - 7.25
20 - 7.27

What is interesting to note is the the best modules were found at the ends. 1-5 & 17-20. The worst were found grouped together near the middle. Its literally an inverted Bell Curve.



Has anyone else ever noticed that behavior in the degradation of the cells?

What am I going to do now..... replace the middle cells #9-15, try a little balancing on the grid charger and hope for the best. I am also considering moving the best 7 outer cells into the center to replace the worst and the replacements I get I use them at the outer spots. Sounds like rotating car tires...

Any thoughts?

 

delete

 

OK I will do so.... Will update you on that next time i pull the pack out. Its the daily driver so keeping it out of play for a few days to check for voltage drop after a full charge may prove to be challenging.

I will certainly start with the ones that "failed" the group test and try testing those individually.

The individual test will run about 10 x as much current drain thru the module than the group test.