2005 still using OEM HV battery, replace now?

Thanks for all the input! I watched a few battery rebuild videos and figured I might as well give it a shot taking the battery apart. Not too bad overall, hardest part(s) were:
1) removing the driver-side trim piece. The long bolt was recessed too far to actually reach with a socket+extension, and the trim wouldn't push in far enough to allow access. So I just ended up bending the trim back to expose the two bracket bolts underneath. Removing the trim doesn't otherwise seem necessary.
2) unbolting the bus bar(?) covering the two main terminals. I bent the bracket there pretty badly trying to get enough torque on the corroded bolt (even with WD40 it was pretty tight); hopefully I didn't do any permanent damage there.
3) actually lifting the pack out of the car (need to work on my deadlift). a moving blanket helped a lot.

Once inside the pack, I took half of the bus bars off and checked blocks 1-8. They all had a voltage of 7.83V-7.86V (very nicely balanced, and serials indicate they're all the same age) with one obvious outlier in module 6 reading 6.60V (assuming a dead 1.2V cell inside that module, out of the 6 cells per module?). So I'm going to try replacing that one with a reconditioned one from 2ndlifebattery.com. I'll try discharging my replacement down to ~7.8V (sounds like I can use a lamp socket like this?) to at least start it off at the same voltage as the others; hope it can also discharge similarly.

I'm hoping the new module buys me a few months while I figure out a longer-term option. I'd like to keep the car maybe 3-4 years but not 8-10, so getting my pack properly reconditioned through a few cycles seems like a nice middle ground compared to a full pack replacement for $1500-2000. Installing a charging harness then hooking up a grid charger seems simple enough at this point. Prolong seemed too pricey so I'd love to know what cheaper options are out there. Just started following: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat

Not sure how well reconditioning will turn out with the new module, I'll have to read up more on the wiki and the repair guide:
Prius High Voltage Battery Reconditioning | PriusChat
Prius Traction battery repair summery | PriusChat

OEM isn't as appealing after I found out the parts warranty is only 1 year if I self-install (so it may not recoup that much in the resale value)

(I may very well become a whack-a-moler; this has been a pretty interesting project so far. I already had my rear seats out for camping I may even swap block 6 and block 1 to make it easier to access from the edges next time, thinking this mismatched pair is likely to go next. I also recorded a bunch of Dr. Prius data that might help me predict the next worst blocks. Looks like #4 is next weakest, distantly followed by #13, #1, #14)

@drone13 Funny you mention the body braces - I was curious whether I'd be safe to test drive the car without putting all the bolts for those back in. Definitely should invest in an impact wrench and a in-lb torque wrench to get the torque right when I put the pack back together.

With used car prices as they are (I saw a 2nd gen Prius like mine going for $8900 on eBay, almost double what I thought mine was worth), it's easier to justify going the long route

 

Some photos of the bracket over the main terminals that I bent up badly. There was a thinner piece underneath I almost broke, hopefully nothing important

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Ah that Ryobi deal sounded promising but it looks like they only offer an impact driver, not an impact wrench: https://www.ryobitools.com/ryobidaysfreetool

I do have a Harbor Freight impact driver that worked okay with a bit-socket adapter (as long as I started the bolts by hand) up until I lost the adapter under the seats :facepalm: Once I can get to HF again I'll probably buy a proper impact wrench there.

Autozone has a nice $15 torque wrench that can do 0-150 in-lbs, so I'll be using that to put my pack together. It doesn't go high enough to torque the compression bolts though; does those need to be exact? I figure since they don't directly fasten any electrical connections it should be okay.

 

Finally got to load test all the modules plus my replacement last night (used Prolong instructions, 120s with my ~50W H4 bulb). Most dropped around -0.34-0.38V from 7.75V but there were a few outliers. Worst one was -0.42V and a pair of -0.40V.

The weakest ones are mostly towards the middle of the block so I'm thinking about moving them to the (fan) end so they're less likely to overheat.

I'm also thinking of separating the two weak blocks so the whole block isn't weak, or would that be counterproductive? Is it better to keep similar-discharging modules paired up, even if that means two weak blocks together? Sounds like there are multiple schools of thought on this: Prius Hybrid Battery Recondition Guide | PriusChat

I'm a bit worried about having this really strong new module (<-0.3V on load test) paired up with an aging module (-0.37V). Should I try to pair the new one against one of my stronger modules (-0.33V)?

Maybe I'm overthinking this and should either get these reconditioned to revive the weak modules (or replace them outright while I have the pack open?) and let a few charging cycles on a grid charger/discharger balance these out naturally?

 

@Kristenbluefin you got a 2012 pack with warranty? Curious where since I hadn't heard of that as an option.

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Also curious, does a module need to compressed just for discharging? I'd like to run a quick 120s load test (with 50W halogen) to make sure my replacement modules are good before installing them in the pack. My impression from reading around is that *charging* the modules is liable to cause them to bulge and become unusable.

On that note, I have one replacement module that's slightly lower voltage than the others (-0.1V) but not necessarily discharging worse. I'm thinking of charging it up briefly with a 3A Everstart "smart" charger (from Walmart) that has a 6V mode and doing another load test to be sure. It's one of these: EverStart 3A Portable Smart Battery Charger and Maintainer with Digital Display - Walmart.com - Walmart.com https://g.co/kgs/TsC3Sv

Bad idea? I'd rather not have to discharge all the other modules to bring them all down to match. 3A also doesn't seem too aggressive compared to the other chargers I've seen on here. If it works it would be nice to keep my spare modules charged in case I need to whack-a-mole again.

EDIT: nvm, I decided to replace the weakest one and discharge the others to match. Got within 0.08v, hope that's good enough. I now have two spare modules I guess I'll just resell or give away

 

So the pack is back in the car with 3 replacement modules and did a few short trips without problems.

Voltage difference around 0.2V but isn't peaking anywhere near 1V like before. Biggest concern I see is that IR slowly rose up to 30 on the same block that went bad before. Hopefully that's not going to trigger a red triangle and the voltage will stay in balance.

Any ideas on why the high IR? Block 6 has the strongest of the new modules from my load tests. Maybe the other module in block 6 went bad after being paired with the failing module? It tested fine in load tests though.

IR was also high with a block I didn't touch (#4) so it's probably something else. I did torque the bus bar nuts to 50 inlb and removed corrosion with vinegar (but didn't use Ox Gard grease, still bare copper bus bars)

They're all fairly high compared to before, maybe a reconditioning would help?

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So the battery is definitely running hotter than before, got close to 125F today. The odd thing is it actually got hotter just sitting parked for an hour, from 110 to 120 when I started it back up. Ambient temp is only 80 and temp rose even after sunset so I don't think it's just a hot cabin.

Fortunately it hasn't hit 130F to trigger a code, but I definitely don't want to run it like this long term. In my testing before this I was usually below 100F. Any ideas what's wrong? I could double-check the torque on my bus bar nuts ( and replace the bars with nickel ones), on the off chance the connections are not as good as before and generating more heat, but I thought I was pretty careful on this. Maybe I should have used ox gard. Or maybe my torque wrench wasn't well calibrated. Or I soaked the bus bar nuts too long in vinegar/salt (overnight) and damaged the threads? They darkened but seemed fine enough to use

I also double checked the fan inlet isn't blocked and felt a faint intake of air there. The fan is working and I cleaned it before reassembling. Don't think I damaged it. Upper and lower air ducts fit snugly (foam wasn't perfect but not sure that would matter) and weren't cracked.

Hopefully I haven't borked my cooling system somehow.

The other odd thing is that the internal resistance isn't actually correlating with the temperature like I thought. This morning temps were low but IR was still high (30) but slowly went down as I drove and temps went up. Curious how Dr Prius computes IR .

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It's been about 8 months and so far so good. Not sure exactly why it's held up well, but the replacement cells seemed to be very good quality. I'm hoping it can get to one year and then I'll re-evaluate.

My OBD2 port seems to be malfunctioning or else I could report on some hard numbers from Dr. Prius app. But the module voltage difference seemed to be ~1.1V last I checked, still pretty good.

Unrelated: my MFD has been flaking out so I guess that's one more thing to fix soon :/

 

So yesterday after about 9 months, I got "Problem" from the MFD followed by a red triangle and two hybrid codes (Pack deterioration, don't remember the other). I was able to clear them and drive home without issue (no limp mode and hesitation like last time); car drove fine with no codes coming back after ~30 mins.

It seems my ECU alerted me a bit earlier than last time; I wonder if I may still be able to drive normally a little longer while I figure things out.

Haven't been able to get Dr Prius module readings yet; my Viecar OBD2 reader has trouble connecting and when it does there is no data (recommended here Hybrid battery diagnostic and repair tool for Toyota and Lexus). Will probably replace that then gather some data first from Dr Prius and decide what to do. Seeing three options:
1) I could open the pack up and replace any more obviously bad modules to buy another 6-9 months. Troublesome but the bad module I last remember seeing was the last in the series so that might help some.
2) Trying a reconditioning charger? Maybe some cycling could help bring the modules in alignment a bit longer. Maybe wishful thinking at this point though.
3) Best option is probably to just put the $1950 OEM pack in there. But pricey and I'm not sure how long I want to keep the car with other problems like the MFD piling up (radio is out). Plus driving a 2005 I'm really wishing I had some features like TPMS, a backup camera, AEB, etc. I guess I'll likely see most of the $1950 back if I sold the car in a year or two? With gas prices and such, it looks like resale is pretty good. Seeing $6-8k for driveable <200k Priuses (assuming original aged HV battery).