Brief history:

Last year bought non running for $1500 CAD, 209,000km (130,000miles). The truck had been sitting 1-2 years in Saskatchewan Canada.

I was able to enable the 300v hybrid system and get it running. Even after sitting, battery voltage was 300V+. Scan tool data logging showed 1 module out of 20 dropping voltage, only under load. High voltage variation code (and service hybrid system) was on.

Drive it the rest of the year and parked it November 2022, starting and moving it occasionally in the cold winter months to clear snow.

Was going to order a green bean battery, but dragged my feet. Started reading prius chat and watching YouTube videos on testing battery modules. Decided to give it a go.

Now.. since reading here I've come to learn GM modules/battery management is horrid and I'm basically wasting my time. It's a good thing this vehicle is more of a fun project than a serious daily driver.

Out of 40 modules I found 1 to be bad. The battery had sat all winter, resting voltage on all of them was 7.95, one 7.94. The first round of discharge was low, 1800-2000mah. Again it hadn't been driven for months. The bad module (#27 discharging only 0075). After 3 cycles all other modules were 4000mah +. Now I'm seeing 4500-5100mah, discharging 1A down the 6.3V.

So that brings me to my question, are these modules in fact horrible? I'm going to run them regardless but I'd like to get some opinions. I'd like to try lithium, but this thing sits in the cold sometimes.

I also wanted to share my data findings on a cold climate 2009 GM battery. I will post my crude hand written on-going spreadsheet. I want to try get all modules close to 5000mah discharge.

The other thing I've noticed after cycling a module and it sits for a week the discharge capacity does drop when I cycle it again, but returns strong after a second cycle. Is this loss in capacity what makes these Panasonic batteries junk? I also realize my hobby test gear has lots of room for loss and error..so there is that too.

Curious what will happen when my new module arrives and I can drive this pack again.

 

130K in a cold weather climate and not abused - I wouldn't be completely shocked if it's serviceable, but I would not have high expectations. Some of the values in your sheet are encouraging.

Please confirm my interpretation of your data:

#25:
7.952V resting
1892 initial discharge - after sitting for a long time... .how long? The full 1-2 years?
7500 charge
4421 discharge following 7500 charge
7500 charge
4629 discharge
6842 charge
Wait 1 week
8.015 resting voltage
3797 discharge
7046 charge
4829 discharge
7500 charge
4888 discharge
7500 charge

What is your charge current?
What is your discharge current and is it constant, or does it change with voltage? - assuming < 2A

I have many comments.

 

Hi Keith. Excited to talk about this with someone. Nobody in my area has any interest in this stuff.

I am charging at 3amps, discharging 1A, but the hobby chargers do vary the discharge current with voltage. When you mention that I realize that would greatly affect how the battery behaves, that wouldn't be the case in the truck itself.

Feel free to let me have the honest truth! You did read my data correctly.

 

The most important piece of information you've gathered thus far is the initial discharge value. Those appear to all be pretty close around 2000Ah. After a 1-2 year sit, you can be reasonably confident that all modules have 2X THAT measured value in total capacity (about 4000mAh), which is great for this car and this battery.

On that basis alone, I would conclude your pack is serviceable AS IS with no additional processing; however, you've started something, and now you need to finish.

Comments:
1) 3A charge is too low. For the way NiMH charging terminates, it's important the charge current is near 1C or 1 X capacity. Capacity is 6.5Ah, so 1C is 6.5A. Given their age and presumed reduced capacity, 4-5A would be preferred. If you can adjust the sensitivity of the chargers, that would be good. Normal sensitivity is 5-6mV/cell. You want to be around 2-3. Good news is 3A is a relatively low current. Little chance of damage. The fact that you're pumping 7500 (I'm assuming a set cut-off) into most of them, but only getting 4000-4500 out indicates the charge termination criteria isn't sensitive enough. For 4500mAh output, one would expect to only put in 6000-6500mAh typically. For charges that terminate below 7500, those are either actual properly terminated charges for false triggers due to a bad connection. LASTLY, for consistency sake, do not make any changes to the process.

1A) your leads suck. Nothing personal. Nobody tells you about this. Recommend you use a zip tie to "pinch" the banana plugs together where they exit the charger. You don't need a lot of force, but you want to put pressure on them to insure they have good and consistent contact. Cut the alligator clips off and use crimped ring terminals - even the cheap ones are fine. Secure to terminal with the nuts that came with them. Torque to 48 in-lb. If you don't have a 48 in-lb capable torque wrench, get one. You'll need it for the assembly. Proper torque is critical.

2) 1A discharge is too low. I understand that you're limited by the chargers. The downside is that your results may not be in any way indicative of their actual rated capacity. #3 will help correct that.

3) buy this: If you already have a digital tester like this that can measure milliohms (mΩ often reported as "mR"), you don't need it, but we'll need to figure out if it will work.

4) DO NOT CHARGE THE NEW MODULE UNLESS IT'S COMPLETELY RESTRAINED. IT WILL INFLATE LIKE A BALOON AND DESTROY IT. DO NOT BE SURPRISED IF IT'S A COMPLETE PIECE OF ****. SO MANY UNSCRUPULOUS/MISLEADING SELLERS.

5) Your spacing between chargers is good. Keep doing this. You need the adjacent untested modules acting as a heat sink. Even at low current, these things can generate heat. If any exceed 40°C, terminate charge. If you can conveniently blow air down through the modules for cooling, that would help.

6) The loss of capacity after sitting for a week is normal. They bleed down fairly rapidly from full charge and then they settle to a very slow discharge.

7) Recommend you conduct the first discharge and 1 charge on all remaining modules before proceeding with cycling. Again, leave your current settings intact to ensure you get consistent results, but apply the zip ties and ring terminals.

The tester in #3 can measure internal resistance very reliably with the proper settings. It may not be absolutely accurate, but it will be very useful for checking for outlier behavior. It will help to confirm that your 1A capacity will translate to usable capacity in the car.

 

Thank you thank you!!

You weren't even harsh 😄

So happy to read you think this pack has some life in it with initial results. Makes my day.

My charger settings were only based off what others used, and what was apparently safe. All of the hobby chargers support 5A charging, some 10A. I hear you loud and clear, will not change for consistency sake at this point.

My leads have bothered me all along, no offense taken. I soldered to the alligator clips and had actually started tightening the nuts to the clips (the setup picture is a week old). I will switch to ring terminals and ziptie the banana connections tomorrow.

The CQ3 charger supports up to 5amp discharge if that helps. I have attached a picture of my multimeter displaying mΩ.. but I think I'm better off ordering your suggestion if it'll help. Unless of course a higher discharge rate solves it.

I will definitely not charge a pack un-clamped. I had gathered that before!! Understood.

I will finish up this last round on these modules and change settings. I am charging to 7500, so I'll bring that down the 6500. Set sensitivity to 2-3mV/cell and charge at 4.5amps? What about discharge amperage? Currently taking them to 6.3 volts.

If I'm better off with the Amazon tester and leaving settings I can shut things down too.

Thank you again! So much muddy info out there on this stuff. Many different opinions, often seems like guys like me trying to preach like they know (which I definitely wouldn't be advising with my knowledge).

 

Do not use that meter for resistance. That's for circuit resistance... not a battery. Battery might blow it out.

More later.

 

Let's look at the results of the remaining voltages, initial discharge and 7500mAh recharge before we make any changes to the process. Leave ALL settings as they are.

Long ago I used a fastener on the alligator clips. It's better than just using the jaws, but ring terminals are far more consistent.

The amazon tester is a 12V battery tester that works on these modules as well. It correlates incredibly well with some dedicated equipment I have.

Recommend you enter the data into this table:

https://docs.google.com/spreadsheets...it?usp=sharing

Save yourself a copy.

 

Sounds good, I'll get a couple more cycles on the remaining modules with current settings.

I was actually going to order new banana plugs and some nice wire and build new leads but I got too excited and wanted to start testing. The plugs were slow to ship to Canada, have plenty of ring terminals on hand so that's easy enough.

Ordering the 12v battery tester now. April 20th arrival, glad to see that'll be quick! Should I be waiting a certain amount of time before reading voltages after?

Edit: I should also mention the chargers NiMH Sensitivity: D.Peak is set to Default. The next lowest setting is 5mv/cell. Don't think I can set it at 2-3.

 

No harm in modifying what you have vs. waiting on new. Given the tedious nature of this testing, anything reasonable to keep things moving is likely worthwhile.

Again, I would stop the cycling and simply do the initial discharge/charge on the remaining modules hoping the ~2000mAh is fairly consistent.

Sensitivity may be as high as 10mV. Again, leave it at default.

How long to wait before reading voltage when?

 

I misunderstood some things,
I do in fact have all initial discharge/charge readings. My original attached photos had them, but they were out of order and numbers were cut off. I have since fully updated the spreadsheet you sent.

Also, my halfway through voltage reading was not consistent at all. Some modules had just finished charging, others had been sitting for a week or two. I originally only had 3 chargers doing 3 cycles each on all modules. Once I finished all 40 modules I measured voltages, then continued cycling again to try bring all modules up to 5AH.

My original black Thunder chargers will cycle 3 times without stopping. The silver CQ3 will stop cycling once 7500 capacity is reached. So as I keep testing, some modules have more cycles than others. That shows which modules have a black Thunder AC charger on them.