Gen II Prius Individual Battery Module Replacement

I thought I would add to this thread since it was very helpful in my own diagnosis. After picking up a mini VCI setup I have to say it because very obvious while watching the data screen what the issue was. I was able to confirm (watching realtime while someone else drove) that I do have one battery bank that is consistently low (likely one module is bad) under heavy usage and is causing the vehicle to throw hybrid battery related CELs. One interesting thing I saw was that while drawing current from the pack under acceleration the bad bank would appear in in the "minimum battery voltage" column but when the vehicle decided the voltage was low enough and went into battery regen mode the bad bank then immediately switched over to the "maximum battery voltage" column (something to look for anyway when you are doing testing on yours).

Here's how to set up the mini VCI:
XP Home or XP Professional with Mini VCI? | PriusChat

Once you have a good idea of which modules might be bad you should order some to replace the bad ones and then disconnect the pack for cycling of individual modules (a pair of 4x chargers can cycle the entire pack in around 3-4 days and all the charger settings are in this thread). The entire pack should be electrically disconnected from the vehicle before any work on it begins. Lastly make sure you have enough knowledge before doing the job or you may end up like post #197 above potentially causing damage to either the vehicle or yourself (yes, this battery can kill if you don't handle it properly). If not you may be better off having it handled professionally instead.

 

Congrats on getting your VCI up and running. It is amazing how useful this cheap little piece of equipment is.

John (Britprius)

 

I've got my battery out, and bad module replaced. The first time I took the battery out the module was only .2v lower than the rest. The code my OBDII gave me confirmed that it was the bad one. The second time I removed the battery another 500+ miles later the module was over 1.5v lower than the others. When I load tested the modules they all dropped .2v except the bad module, it dropped over 1.0v. I've completed charge on the first 4 modules and the next 8 are cycling as I type. It's taking about 20-26 hours for them to cycle, so they should be done by saturday morning and the battery should be back in by saturday afternoon. Everything seems to be going smoothly. As long as it works (and it SEEMS as though it's going to) I may post a few DIY videos on youtube and put the link in this thread. I've also thought about getting one more 4battery charger and 2 single chargers so I can do an entire battery in 2 days and refurbish more.

 

It's taking quite a while to cycle through all the batteries even with 2 quad chargers (I'm using very conservative settings with 2A charge rates) but I thought you guys might like to see what it looks like to work on a Highlander Hybrid too. I made my own leads from some extra Monster speaker wire I had lying around. One other pain is the battery packs are riveted together so if you need to replace one it's not as easy as just undoing a few bolts. It's definitely more work even getting the batteries out of the car than a Prius, but overall the general principle is exactly the same.

 

2amps at a high SOC is not a good idea for these cells. Fun pics though.

 

Eric, I appreciate the input but I'm not sure what you mean because I've seen people in the thread using 5A at high SOC cycling without much issue and I'm using 7000 mAh capacity with 2A charge and all are returning 6000+ mAh when discharged to 8V (this is with 250k kms on the vehicle odometer).

 

You can do it, I wouldn't though.
I have seen the posts about 5amps at high SOC and it makes me cringe. If you have time to do it right, then do it right.
Better to taper the voltage at the end of a charge. This is true of almost any battery chemistry.
If your equipment can't do it automatically you should do it manually.

I enjoy discussing battery theory with people in person, but I'm not very good via long rambling threads/posts.
What you are doing is probably fine to do with your own experiments on your personal vehicle.
I just would not do it that way for other's packs.
Make sure you keep things compressed and well cooled.
It will work good enough for your situation.
Sorry to confuse the issue.

 

No worries at all and I certainly appreciate your experience on the subject. My batteries are very well cooled and it's still near freezing here (batteries don't even get warm at all when charged to 7000 mAh with 2A.......no noises from the cells either). I also leave them clamped in the metal frames while the cycling is taking place. I did try 5A, 7500 mAh rate on a spare test module before starting the project, but my lack of understanding on how my charger worked (did CHG>DCHG instead of DCHG>CHG) and imperfect clamping is likely what destroyed that one (ie didn't start cycle on discharge so it likely went well above any reasonable capacity limit and ballooned the cells out). Luckily this was enough of an eye opener for me to scale back the capacity and charge rates to what I am currently using. I need to read a bit more about these RC chargers and see if the current tapering is in fact a feature it is using without me knowing it. Thanks again for sharing your experience on the subject.

From what I understand did you recommended less than 0.5A charge rate at the higher SOC?

 

Sometimes it is an automatic function. NiMH has a very specific charge curve. Most of the chargers should have at least one program setting that follows this. Of course there is usually an manual user override function as well.

 

Yes, my charger was set to charge using the NiMH function so hopefully this tapering was being done automatically for me during the cycling process.

 

Good to hear. There really is no reason to slam 5amps, or 2amps into a cell at high SOC if your charger has the ability to taper at that level.

 

Got the battery back in my car today. Took it for a test drive and just before pulling back in the drive way I got P3019 (battery block 9 becomes weak) it was 8 before. I'm 99% sure I put then back in the same order. Here is my question... Does anyone know how these battery modules are numbered within the battery? THANKS!

 

What you describe is not an unusual phenomenon. Depends on how well the new cell plays with the others.You may end up playing "whack-a-mole" a little bit until you really sort all the issues with your pack.

Sounds like you are certain you put things back in the same place?

 

I am, I kept them in the same order as I took them out. The "bad" module was obvious. NONE of the others dropped much under load and were all within .1v when I tested them before removing any from the pack. I'm sure I replaced the correct one. Any thought as to why it would say another module is "weak" now? I'll be pulling the battery out tomorrow and checking them all again with my multimeter. I also took some pics of the process that I'll post tomorrow.

Side note, when I hooked them up in parallel it took maybe 2 hours for them to "equalize" to within .01v I disconnected them after 4 hours because they hadn't changed in the second 2 hours. Shiuld I have left them connected longer?

 

Initial tear down.
My charging setup.
Final balancing (or so I thought).

 

I agree with Eric that this isn't uncommon and it has alot to do with how the modules work together in pairs (banks). It is key to also have a mini VCI setup so you can watch for potential issues with all the modules while in use (esp while accelerating) and play around with different configurations to be sure they all provide similar voltage readings while under load and while charging. Not looking forward to this part myself as the 9.6v modules for the Highlander are alot harder to obtain than the 7.2v ones for the Prius/Camry.

I know the suggestion has been put out by some battery re-builders to take the modules from the center of the pack and move them to the outside and vice versa (in testing capacities I can see a linear difference myself, likely a result of heat distribution since the center modules are the most difficult to cool in use......sort of like rotating a set of tires to get even wear). Seems to me it would also be ideal to take the lower capacity modules and pair them with the highest capacity ones (found during testing) since that way the banks (module pairs) should be better balanced for overall capacity. The other possible solution I can see would be to just invert the 2 halves of the battery to put the lowest capacity modules on the outside where they can be cooled more efficiently and hopefully the capacities will even out well over time.

For example:

If I have 8 modules come out of the vehicle with 6200, 6150, 6100, 6000, 5950, 6050, 6150, 6250 mAh

1. Is it better to put them back into the vehicle with an order like 6000, 6200, 6000, 6150, 6100, 6050, 6250, 5950 mAh (giving you average bank capacities of 6100, 6075, 6075 and 6100 mAh respectively). My thought would be this would give the battery ECM the most even distribution of volatge under load (ie minimize the weak bank error codes)
2. ......or would it be better to just inverse the original order like this 5950, 6100, 6150, 6250, 6200, 6150, 6000, 6050 mAh (giving you average bank capacities of 6075, 6200, 6175 and 6025 mAh respectively.......eventually over time/use/heat distribution I would expect them to level out again provided you don't get any weak bank codes in the process).

I'm sure the battery gurus out there could comment on which would be better or whether this might not work at all and why.

I don't think this likely caused your issue but I would let them equalize at least overnight just to be safe.

 

I think my problem was... I cycled all of my modules at least 3 times and more for those who took some extra time getting up to the 7250 mah BUT I didn't match the discharge cycles well. There are some still in the low 5000s some up in the high 6000s. I believe even one or two were still in the high 4000s. I've began re-cycling the modules that had low discharge mah. Where do you guys THINK they should be? What would be the optimal mah balanced between the two modules in a "BLOCK"?

 

oh... and which modules are match together in a "Block"? 1&2 3&4 ect...?

 

I'm not an expert but, it makes sense to add all your module mah up and divide by 28 to get the "average" mah of all the modules. Then, I'd try to make every block 's capacity equal to that (or as close as possible). Does that make sense?

 

What I did was to cycle each module 3 times D>C at 7000 mAh (first discharge tells you the state of the module coming out of the car, the second and third tells you what the total capacity is at high SOC and helps to exercise the cells back into shape). Then once that was done I would do a final D>C cycle at 4500 mAh, but make sure you discharge the cells initially so there is less than 4500 mAh when the cycle starts (usually I just discharge the cells below 4000 mAh then start the cycle again). If you don't discharge it below 4500 mAh remaining the charger will complete the cycle, but the voltages will be off considerably since the battery wasn't pulled down to the 6V (8V for Highlander) minimum before the charge cycle starts. If you follow this method it makes sure they all have similar starting voltages before final balancing.

I also wouldn't suggest going much above 7000 mAh when testing since I don't think there is any benefit and the risk of heat damage increases considerably. I also think it helps to keep the charge amperage as low as possible (I use 2 amps max), this becomes more important the farther above 6500 mAh (nominal capacity) you go. The lowest module I found so far was in the 6000 mAh range and the highest was around 6350 mAh so I think for the most part the cells are fairly well balanced. I'll need to see how I do once I get them back in operation though.