2005 still using OEM HV battery, replace now?

I have a 101k 2005 Prius still using the original HV battery. It still drives fine (~45mpg if mostly highway, less in city), but the HV battery seems to be getting weak. I haven't gotten a red triangle yet, but lately the SOC in the HUD seems to often be in the red when I start the car, and just today it went from green 7/8 to red 2/8 driving just a block or two.

I connected my OBD2 with Dr. Prius and took it for a drive, but the cells don't look too bad as far as I can tell (see attached screenshot, taken after a drive). The voltage difference stays around 0.10V and no one cell seems to be consistently low. The IR values were 19 milliohms cold and 25 milliohms after driving. Is that the best metric to keep an eye on? I read 30+ is when I should expect a P0A80, right? Is that the point at which the battery is likely to leave me stranded?

I know a red triangle is coming someday, so I'm wondering what I should be looking out for (in Dr. Prius or otherwise) and at point I might expect the HV battery to cause me to get stranded and need a tow. If it's at a point where it's months away (and beyond saving with a Prolong charger?), I'm thinking might as well replace with a 2k1toaster battery. Part of me wants to hold out for the new lithium-ion batteries if I can though.

Side note: anyone in WA that would be interested in the used modules when I do replace mine?

 

Appreciate the advice everyone. The SOC lately is almost always red in the morning and was at 1bar or ~35% after 2 days not driving (noticably hesitates when accelerating) and the voltage difference is now closer to 0.2v at rest. I'll wait until I get a red triangle to replace it, but I'd be surprised if it lasts another year with how it's been worsening lately.

I'm really curious about is if it's the one bad cell at #6 or not. The voltage difference rises a lot when I'm accelerating (around 1v+, see Dr Prius screenshot), so it seems like the #6 cell is lagging behind the others when under load.

I'm tempted to just swap out a single cell myself (maybe clean the battery fan and bus bar contacts while I'm at it) and see if that buys me some time given the other cells seem to be well balanced. Any pointers for testing a replacement module besides just voltage? I see local and ebay sellers have them going for $20-35 each but there's little info on quality. It seems like a bad idea unless I can be sure I have a good module, plus the tools to properly balance it post-install. For the latter maybe something like this but I'm not sure I have the savvy for it: Build Hybrid Battery Maintenance Gear For Under $100 | Page 3 | PriusChat



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Maybe OEM is the way to go. I read people were getting the OEM battery for $1650 late last year?
GreenBean is offering LIFETIME WARRANTY!?!?!? | Page 6 | PriusChat

Is that still possible these days? I'm seeing $3165 now (unless I can get a $1350 core charge off that? 3165-1350=1815?):
G951047031 - Toyota Battery assembly, hv supply. Electrical, wiring, cable | Toyota of Lake City, Seattle WA
G951047031 - Toyota Battery assembly, hv supply. Electrical, wiring, cable | Heartland Toyota, Bremerton WA

 

Sadly I got my red triangle of death today. Codes were P3000, P0A80, and P3016 (module 6, the same one as was weak in my OP 2 weeks ago). Module 6 was reading about 30 milliohms IR at the time of red triangle (I think I read this is the threshold that triggers the code?). Voltage difference seemed to be as much as 1.5V between the bad cell and the others.

I was able to limp the car home but only barely (fortunately not much traffic). At times, acceleration was much much weaker than normal and the car would fail to accelerate past 25mph or even 15mph even when the engine seemed to be working hard (high rpms but no torque). Brakes seemed less effective than usual (disabled regenerative braking?) Clearing the codes temporarily got my acceleration back to normal but not for very long. Wouldn't feel comfortable driving this much since the red triangle seems to be coming back within 5-10 minutes.

The HV battery fan in the rear seemed to be working continuously. Battery temperatures were around 104F (seemed to peak around 122F at one point coming back but Dr. Prius wouldn't update the data in real-time like it normally does) but I didn't get a code for battery overheating. Would these temperatures be enough to cause damage to the rest of the battery (likely sustained 30min)? If that's the case then swapping out just one module seems like a lost cause. Before this had happened, my temperatures were reading around 80F.

Debating now between the OEM replacement (found a dealership who can do ~$2000 for the part) and trying my luck with replacing the bad module (6) with a used module from a local or ebay seller. Voltages on the used modules seem okay (7.6V) but not sure how they'll play with the rest of the pack. I may try cleaning the battery fan in case a clogged fan is aggravating the problem, but that seems like a long-shot. If that was the issue the damage was probably already done

Any pointers for making the car more drivable short-term? I wasn't expecting the car to lose so much power so quickly once I got my first red triangle.

PS I do have a mini-VCI cable in case there's something more I can do with that+Techstream which Dr. Prius cannot.

 

I found a dealer in PA that can do ~$1600 but not sure I can get that price-matched locally. I got the pack mostly out today and got the fan cleaned out (dusty but not clogged), wasn't too hard.

Just changing out a $30 module for now is tempting though; Block 6 is definitely the outlier here according to Dr. Prius voltages and the others look pretty well-balanced.

I'm curious - would I want to swap out both modules in block 6 or just the worse of the two? I read something about one module causing the other to reverse-charge and also get damaged, but in the repair videos I've seen usually only the module with the lower voltage needs to be replaced.

 

Here are some Dr Prius screenshots. At 34% I actually see higher voltages (17.5V-18V) compared to 60% (15.3V-17V). So I'm not sure what good modules' voltages should be, 8.5V?

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Ok I'll follow up on a new thread

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