HV Battery Failure: Anyone With Troubleshooting & Repair Experience Willing to Offer Some Advice?

Hi! First time poster, though I've learned quite a bit already from these forums since buying my Prius back in May.

Background: 2008 Prius, third owner, 209k miles (15k of which are mine)

Problem: Last week, I started getting the dreaded red triangle of death and codes P0A80 and P3000 (hybrid battery pack deterioration & high voltage battery fault/malfunction). I kept driving it locally a little bit (maybe 30 miles), cleared the codes after it started handling very oddly (very similar symptoms to those described in Prii Newbe's comment here), and soon enough we added P3014 (HV Battery Module 4 fault/malfunction) along with the new-to-me P0A78 (drive motor A inverter - performance problem). Note: I am assuming the latter problem is just a symptom of the battery issue unless someone tells me otherwise.

Diagnostics: Dr. Prius confirms that Block 4 is the problem child. Here's what the voltages look like when I've just started the car:

Voltage After Starting Car by thenightmareofhair posted Jan 22, 2022 at 12:50 PM

And under load (rear defroster, headlights):

Voltage Under Load by thenightmareofhair posted Jan 22, 2022 at 12:50 PM

Research: I've dug through a lot of information here, on Reddit, and on YouTube. Guides that I've found particularly helpful are:

1. ChrisFix's guide to full battery replacement (YouTube)
2. The Ultimate Guide to battery module replacement & battery reconditioning (YouTube)
3. The wiki entry with notes on reconditioning, rebalancing, and replacement (PriusChat)

Options: I have access to basic mechanics' tools through a local makerspace lending library, but nothing in the way of electronics with the exception of a volt meter. I've narrowed my options down to 6 levels of investment, listed here from highest to lowest cost:

1. Full OEM replacement from dealer ($3,000)
2. GreenBean full replacement + installation with 3yr warranty ($1,600)
3. Full set of 28 refurbished modules on eBay with 2yr warranty, self installed ($650)
4. DIY module replacement and full reconditioning (~$375 and 1-2 weeks, including maybe 2-3 days of actual work time)
5. DIY module replacement and voltage rebalancing only (~$125 and two days, including 1 day of actual work time)
6. DIY module replacement only (~$100 and one day)

I'm pretty convinced that Options 1 and 2 are not a good use of my limited cash, especially since the car would also need other work within a year in order to pass emissions and/or resell. So my questions are mostly related to options 3-6:

1. Full set of 28 Modules on eBay (Option 3): Would you consider the "full set of 28 modules" option from "thehybriddoctor" on eBay, who seems to specialize in Prius batteries and has 100% positive feedback? Is a warranty from an eBay seller actually worth more than the (metaphorical) paper it's written on?
2. Finding Non-Trash Modules Online: Where does one find reputable/good modules? (And what makes them "reputable" or "good"?)
3. Finding Best-Fit Modules Online: Is it possible to search for a module that is a good match for my existing modules in any way (including voltage) using the online description alone in the hope of minimizing the need for rebalancing and/or reconditioning? I notice some eBay sellers saying things like "7.8-8.0V" but I can't tell A) whether that's resting or under load, and fully charged or not, or B) whether I should be comparing that to either of my two voltage numbers above -- my blocks, except the bad ones, seem to show about 16.3V resting and 15.0V under load.
   
4. Picking the Right Module In Person: The dealer who sold me the car has a ton of spare parts lying around (including old modules) and may be willing to let me pick out my own. (He's a decent guy and I think he honestly wants to help me with this, but he lost his other mechanic a little while back and has a 4-month backlog of jobs.) If he agrees to this, what can/should I do to test the modules in the field and pick the best fit for my car? Should I perform any additional testing on my own battery first (other than the Dr Prius values shown above) so that I have consistent baseline numbers of the "good" modules to compare with?
   
5. Reconditioning vs Rebalancing: Is there any consensus on the importance of reconditioning, or on the additional lifespan it provides versus a simple replacement and/or rebalancing? I ask because acquiring the chargers / power supply / load plus all the extra time & potential for error involved seems like a big extra investment to me, almost on par with Option 3 (eBay), and I haven't really seen anyone quantify (or even qualify, really!) the clinical/practical significance of reconditioning. You have some people who do the process very rigorously, even without replacing new modules, and others who just replace a few modules and seem good to go.
6. Rebalancing: Please help me understand rebalancing! I am honestly inclined to try to avoid even this small step because I can't find any consensus on how to do this properly or whether it's useful. The Ultimate Guide has a voiceover to the original take which says to connect the modules in parallel and then just leave it for 24 hours, but some people say that's proven to be a waste of time and it will fall back out of balance very quickly. Also, does the "rebalance by connecting in parallel" instruction mean you literally just rewire everything in parallel and then let it sit for 24 hours? Or do you have to put some kind of load on it?

I appreciate any and all advice and experience you would like to share! If you are giving advice, I would also doubly appreciate it if you could mention whether you've personally done any of the DIY processes (module replacement, rebalancing, or reconditioning). Thanks in advance

 

Quick update: I am most of the way through this repair and ready to reinstall my battery! (Likely two days from now. It's raining today & tomorrow and perhaps I'm being overly cautious but I don't want to move my battery back from my apartment to the car in the rain.) Things have gone "reasonably well" so far and I will post a detailed report 1) after reinstall, and 6) six months on.

One question I have for those of you who have removed & reinstalled the battery (@AndyFromWI et al): Does the computer automatically recalculate the voltage when you turn the car on and remove the codes on its own? Or should I expect to have to clear the codes via my code reader no matter what if I want the red triangle of death to go away?

Thanks!

 

Is this the case even if I removed the battery (nearly) fully charged? I have not done anything to discharge, recharge, or recondition it aside from swapping the bad module; all modules are now at 7.9-8.0V.

 

Okay, it's time for an update! I will post separately below because I want to include some links to resources and PriusChat won't let me do that without first having 4 posts under my belt.

 

Thank you for all the advice, PriusChat! Here's an update on my HV battery:

Bottom line: I ended up swapping the bad module myself. It cost me $73 and 14 hours of my time. I've driven my Prius about 50 miles since then (both around town and highway driving), and as far as I can tell the problem is completely resolved. Codes are clear, car handles normally, HV battery capacity indicator fills and depletes at a normal speed and mostly stays mostly full... Needless to say, I am super happy with the result! I will post details in my next comment

 

Details: Cost and time are broken down in the 2nd & 3rd worksheets here. I wanted to be honest & realistic, so I included things like tool borrow/return time and bus bar cleaning supplies. I have some generic home improvement / tool experience but minimal electronics and auto experience, so YMMV (greatly). I was also able to borrow all the tools from friends and my local maker space, which was obviously huge. You can see the notes I took on my research and the items I ended up using here -- but they are in notes-to-self format so they include things like links to the local maker space lending library, which will probably not be helpful to you unless you happen to live nearby.

Discussion:

• At the end of the day, after a good bit of research, I concluded that I couldn't justify the added time & expense required to do a full reconditioning of each module. It just wasn't clear to me that there was any good info out there supporting a substantial extension of overall battery life vs just swapping the bad module. I'll try to remember to follow up in six months to let you know if I still stand by this decision.
• I primarily relied on the ChrisFix video, which is both incredibly helpful and also just way too fast/flippant at points, with lots of cuts that gloss over difficulties and a few things that don't seem to be best practice. In my notes doc (second link above) I recorded my own modifications & departures from the video.
• I'm only getting 39mpg right now over the past ~50 miles, down significantly from 45.5 when I was on the road this summer/fall and 43 ish when I came back home in the winter but before the battery started throwing codes. That could just be due to weather / type of driving / not enough new data, but it's something I want to keep an eye on.
• I kind of regret going with a "reputable online seller" of refurbished modules ("reputable" meaning "a few people on PriusChat said the source is reputable," which is unfortunately as objective as it gets as far as I can tell). The 2ndLifeBattery replacement module that I bought may end up lasting a long time, but it is a little worrying to me that it ended up being one of the three modules in my set that settled out to a voltage of 7.9 after a few days, versus the others which had a resting voltage of 8.0. (Per-module voltage measurements, including the new one, are noted in the first link in this comment.) I know there are other measurements of module strength, but I don't like the fact that the module was advertised as "8.2V but may arrive as low as 8.0V because the modules naturally discharge voltage" and ended up being 7.9. Because I took some time between removing the battery and actually working on it, the other modules also had a few days to "naturally discharge" from when I removed them (all around 8.1V per Dr. Prius) but the discharge was notably less.

All in all I am really thrilled with how this whole thing turned out. It's just very empowering to be able to fix your own stuff, and I'm really glad I didn't shell out hundreds or thousands of dollars unnecessarily. Happy to answer any questions, and I will try to remember to add a six-month update as well!