Hybrid Battery Troubleshooting

What were the error codes?

 

clean the corrosion first, and replace the sensor wire

 

^ This.

May as well find out for what reasons (out of the couple hundred possible) the car has shown the triangle, before just starting to do things.

 

And I'm willing to look at those battery module voltage and capacity numbers, but my morning coffee hasn't kicked in so would prefer a frame of reference before going too deeply down this very familiar rabbit hole.

 

The voltages of the 28 modules are all over the place. A static reading of healthy battery modules should not vary by more than 0.10 volts of each other. My guess is that the trouble code that occurred was P0A80 " Replace Hybrid Battery Pack".

 

That's common if a failed battery pack sits for a while. As in this these numbers may be just self discharge data. As in modules that have self-discharged the most should be noted on the spread sheet to further the pack diagnosis. There's a dozen additional types of data points for evaluating a module/pack you can read about on PriusChat.

Resting voltage isn't as good of a data point compared to module voltage loss after 2 minutes under load from a 50w/12v bulb.

But this is just preliminary data... I'd like to see a charge and balance of the pack as well as a couple of deep cycling of the pack before drawing any conclusions beyond the replacement of failed or hot-running cells.

All this and more is how you'll find the bad modules before they find you.

 

Holy bejesus. I can't believe not one person has been able to give you the answer you seek. In regard to the postings above, the OP stated:

"The triangle came on a few weeks ago, and since then I’ve noticed a loss of acceleration power and the fan running loudly in the back."

Which means the battery had probably not been sitting for months before getting his voltage readings.
Yes, your voltages are all over the place. Yes, any module that is under ~7.2v is bad and anything that has drifted down to ~7.4ish will likely be bad very shortly. A module that can be salvaged and become reliable does not drop below 7.2 volts for months and very good ones will stay 7.6 or better for several months. All the ones in the 6's? Toss 'em. They will never be worth putting back in your car. The others that are less than 7.4 may or may not be salvageable, but with the number that you need to replace, it's not worth the risk.

 

..., cost, or effort. Mostly the effort. There is a lot of time and patience required.

The hardest part in all this is having the quantity of replacement (years-old) modules that you can match to the existing (years-old) modules you currently have in your battery. The incoming modules need to have a very close capacity first and foremost to successfully rehabilitate a tired old battery pack.