Dying traction battery?

Yes, you don't want to start fiddling, certainly not yet. If you have TechStream, you should run an active load/stress test on the HV battery. You can usually get a garage savvy in Prius hybrid to do it for $50. If your not pulling codes, you're likely ok. How is the gas mileage?

 

Yes, this is one sign of a weak pack. You might consider the option of grid charging but (IMO) you and other gen 2 owners should have already been doing that by now for maximum benefit/cost ratio. Rebuilt/refurb packs sometimes advertised as "new" are a gamble and only worth what their warranty (and company) will do as they will fail too.

See the link in my signature to see what I did when faced with the same scenario.

GOOD LUCK!

 

Once you know you have a bad/weak battery, you have a number of options. A lot depends on your mechanic capability, how long you want to keep the Prius, and your pocket book. When it comes to the "triangle of death" take your time getting a good diagnosis or you could pay dearly.

 

Going by the voltage readings, once the delta between blocks 1 and 12 becomes too great, a P0A80 code could activate and ultimately turtle mode.

 

Once the difference between upper and lower voltage values becomes too great, the battery computer will trip the fault codes and if the delta is large enough (one or more module failures), protective "turtle" mode will activate shutting off the EV part of the equation and only allowing the ICE to run and power the car which it isn't designed to do by itself (hence turtle mode).

Yup, that answer is different for every person encountering due to many factors. In my case, my 06 has very low miles and I want it to run as reliably as possible for several more years so I went with a new Toyota battery.

GOOD LUCK!

 

I did some extensive reading on the subject and found some owners who have allowed the car to warm up for a few minutes in the morning before initial take off. This seemed to keep the battery from draining. I was experiencing the same situation (with my 2008) that you have with your battery. A quick discharge down to one purple bar and then back up to six within about 6 miles. The discharge was happening while the engine was running and the car was in motion. Now that I let the car warm up a bit, the problem has completely disappeared. This was a problem that only occurred first thing in the morning after the car had sat overnight but oddly enough, never had these symptoms when leaving work in the afternoon. I have a 44 mile commute each way - all open road commuting to and from mountains and valley.

PS - I also have a 2005 Prius with the (completely) original hybrid battery now over 325,000 miles!

 

That actually is not true. During the 50 or so seconds (assuming the A/C is off), there is a small amount of charge going into the battery. But this is not the primary reason for waiting for the engine to cut out (as it passes from stage 1 to stage 2 of the Prius warm-up), it is to allow the ICE to participate in driving the car which, once in stage 2, it will do, but it does not do while in stage 1. Stage 1 is primarily focused on getting the ICE and cat warmed up as quick possible, and while this is going on, the electric motor primarily drives the car. This is why the HV battery can discharge quickly if driven in stage 1, especially if that HV battery is starting to get towards its end of life.

As explained above, while the ICE is running, it is not contributing a lot to provide motive power.

See the link in my signature to read more about the 5 stages of Prius warm-up.

 

Wonderful! Since I am up near the Canadian border, I can get away with not using the A/C for now. It seems to be well document that extreme heat is the worst enemy of a traction battery. When I start the car, I turn the temperature up enough for the ICE to kick on and let it run 4 - 5 minutes before I leave. I know that the battery in our '08 with 180,000+ mi is weaker than the '05 with 325,000+mi because the '05 does not need this warm up. It's a temporary fix but it will extend the useful life of the battery. The only difference between the cars is that '05 was purchased new and the '08 was purchased used.

 

Mine was doing the same thing. I bought the Prolong Hybrid battery charger and the discharger
And did a very mild discharge and so far a year later the battery looks like it’s brand new.
Ymmv.

Your going to have to do something as it will soon throw a code and then your done. It’s either new battery or whack a mole repair.

I bought the original system that uses the light bulbs to discharge. I think it’s s good nvestment because I can easily sell it down the road.

 

When I bought my first prius (a 2005) almost 5 years ago, it had over 200k miles AND it had been sitting for half a year. So it's battery was sorta week. I had a routine, I would hop in the car, push start, quickly depressed the gas pedal just enough to start the engine (didn't want to wait 7 seconds.. I know) let it run while I put my seat belt on, plug in my phone. I would then pull away and gently keep it costing trying not to take much energy from the battery. It would pretty much stay at 6 bars with that routine.