My 2nd HV battery died one week after warranty ended.

Such a tale of woe... But this time I'm going to do the battery repair myself. (I am a retired Electrical Engineer, after all.) My buggy has now racked up 265K miles. The original battery lasted 222K miles, and the repair guy swapped my battery out on a Sunday afternoon for $1500, giving me an 18 month parts and labor warranty. Subsequently, I acquired Techstream and cable, and have been monitoring the cell packs ever since. One module pair (No. 8, almost in the middle of the battery) has always been suspect, and sure enough, one of its members was the culprit for this failure. I only own one car, so I ordered two modules from the internet and tried to time my disassembly to coincide with the parts arrival. When the replacement modules did not arrive on the promised day (actually, only the tracking number was issued on that day), and the items were not given to the Post Office until three days later, I found myself with an opened battery and little to do.
So, I examined the data a little further. I found:
1. The serial numbers of modules at positions 1, 2, and 7 were substantially different from the remainder, and seemed, at first glance, to be generally healthier than the others (higher voltage). However, #2 module's output fell more rapidly than all others, about two times faster.
2. As you approach the center of the battery, the resting voltage of each module seems to degrade slightly, implying that the central modules are being stressed more than those on either end of the stack.
3. The higher stress in the middle theory is bolstered by the Techstream reports that I had accumulated over the one-and-a-half years that the battery has been in service. When the battery was discharging, the lowest pack voltage was found in the middle, and the highest voltages toward either end. When the pack was charging, The exact opposite was true. The weak packs in the middle had the higher readings.
Based on these observations, I will:
1. Discard the failing module, which is number 16.
2. Move the currently healthiest modules (1 & 28) toward the center of the battery, replacing modules 15 & 16.
3. Replace module 7 with module 15.
4. Save module 7 for possible emergency substitution in the future.
Before installing the replacements, I intend to condition them to match the current average, after a discharge/charge cycle performed by my HItec X1Pro charger.

The modules arrive tomorrow.
Any thoughts?

 

I have considered buying a grid charger (with discharge capability) but tabled the idea. Now, I guess I'll have to get more serious about it.

 

I did drive with TechStream hooked up, and verified the failure. As I said, I have been monitoring that module pair since the new battery was installed. The static testing of the individual modules so far has only involved monitoring them for voltage droop over a 3-day period. I will do more voltage measurements before reassembling the complete battery pack.
You are right about the fan. Last time, I cleaned it very thoroughly... each vane... until it shined.

 

Look for "Prius Hybrid Battery Repair" in the D.C. area.
"If you are located within 300 miles of the D.C. area, we will replace your Prius Hybrid Battery in your driveway and have you driving again with a full 12 month warranty on parts and labor.
And that's not the good news.....
No need to pay a dealer $4,100.00 or more (plus towing) for the same warranty that we offer
We can re-build your existing battery with new cables and cells, or replace your battery with a re-manufactured Toyota Battery.
In addition, we can replace your ECU or Inverter pump.
We have added the Camry and Honda Hybrids to our Battery inventory. Thanks for your support and referral business. Watch for our new location in Southern Md. We come to you. Please do NOT tow your Prius."
I live in Southern Maryland. I got an extended warranty because I did the removal and re-installation myself. (And I cleaned the battery cooling fan.)

 

That is just what I observed in my limited sample (my one Battery), as I observed it while driving and standing still in the garage.
It was my understanding that Toyota maintains the battery between 40 and 80% SOC range. And that was what I thought that I observed when I watched the TechStream display. But, it's hard to keep close track when there is so much changing data to look at. Talk about texting while driving!
I am a retired E.E. and have considered making a "poor man's balancing system" for the Prius. I started gathering the wherewithal for my project when I got stiff-armed by HItec. They would not give me the USB protocol for their X1PRO charger. I started reverse-engineering it, but had too many other projects to stay with it. My design would replace the top cover of the battery, hook up to all the modules, and do all the discharging and recharging, while constantly blowing cooling air. My control computer would step a relay bank to operate on four widely-spaced modules at a time, using adjacent non-active modules to act as heat sinks. The computer would keep data on each of the modules as it interfaced with the "smart" chargers (that is why I need the communication protocol.) After the modules are all left in their maximum state-of-charge condition, then they would be placed in parallel for sufficient time to allow them to equalize. It is an interesting project, and I may consider taking it up again. I have enjoyed many projects like this over my 38 years working for IBM and Lockheed Martin, and I sort of miss it after retiring 11 years ago.

 

I do indeed intend to run the recommended discharge/charge cycles. My charger will calculate the true capacity of the module and will graph the voltage and current of the cycles as they occur.
Thanks for the tip on the serial numbers. My 70-year-old eyes are not as good as they used to be.
I was considering replacing my trusty (not rusty though) 2006 Prius when the new Prime Plug-in is available, but I see now that it is only a four-seater. With grandchildren starting to arrive, I don't think that will be enough.
So, I guess that I will have to seriously consider getting a grid charger for this buggy.
Thanks again,

 

If I had had that information 18 months ago, it might have influenced my actions for sure. But, I only have this one vehicle, and urgency was a major determining factor. It is now, too. I am chewing my fingernails waiting for the replacement modules to arrive... today, I hope.
And... I have been following the Plug-In news with great interest. The first iteration was hardly worth it, but the new Prime machine held a lot of promise until I learned of its reduced carrying capacity.
I have maintained this vehicle aggressively, replacing the muffler with a stainless steel one, front wheel bearings, and both front and rear brakes, rotors, and drums. I have also replaced the dust shield panels under the car when necessary, added a trailer hitch, and EV-activation switch. I like the space that I have under the rear floor for handyman tools (always prepared), and the actual spare tire instead of a repair kit. My steed has quite a few war wounds, dings, and small dents, and the touch-up paint bottle in the glove box has seen its share of use.
I am quite disappointed with the HID headlights' longevity (or lack thereof), and have changed them more often than I care to admit.
I recently installed a new garage door opener, and my 2006 Homelink cannot mate to the newer communication protocol. So, I have to use the new remote instead. No complaint about that, though. It's fine.