I think it's happening

Techstream would be the best option and, if you have an old laptop, the cheapest. Lots of threads here about it and lots of buying sources on Amazon and Ebay.

If you plan to keep the car long term, a new battery would be the ultimate answer. But at this stage, a Prolong grid charger would be very likely to buy you several more years of good service from that battery. Lots of people here have gotten great results. Of course, ymmv, so there is always some risk in that option.

If you do keep the battery and re-balance it, I'd suggest that while you're in there, to check all the buss bars and other connections for corrosion. Problems there will eventually throw a code, so it would just be preventative maintenance right now.

 

There's an initial installation that isn't terribly difficult. It might take a couple hours for a first timer with average skills. Jeff provides excellent instructions. Once it's installed, it's plug and play. The cheapest model with the light bulb discharger (what I have for my wife's '07) takes careful babysitting. But the automatic discharger is super simple -- but pricier.

 

This is not a sign of a dying battery, but of a battery that has lost capacity and is in need of reconditioning... Toyota could of built a reconditioning system into their vehicles, but instead they designed the car to run normal even when the battery is only at 50% remaining capacity.

You can restore your battery capacity to as much as 96% of original by cycling the battery, which means doing several increasingly deeper discharges then charge and re-balance. You can recondition the whole pack at once without removing it from the car with a Prolong system/ grid charger.

Or even more thorough, you can recondition each of the 28 individual modules using regular headlight bulbs and RC hobby charger that's designed for NiMH batteries. Doing each module individually is more ideal if you want to find soon to fail modules before they fail... But in general both of these methods combined is the most thorough, but time consuming and the gear is going to cost a good chunk of money and then there's downtime to the car.

One alternative to avoid vehicle downtime is to buy a second used battery pack, sometimes they sell as low as $50 at wrecker, and then work on that pack and once it's ready swap it out and work on the one in your car.

Lastly here's the basic science behind why NiMH batteries lose capacity: BU-807: How to Restore Nickel-based Batteries – Battery University

 

My '06 with 127k goes down to 2 purple bars all the time, usually in city driving.

 

On a good battery you shouldn't ever be going into the purple zone in normal driving.
That would imply heavy driving load with no braking or recharge time, like going up a mountain, or maybe pulling a trailer and you have the A/C blasting.

There are other ways to get the codes too. Some auto-parts stores might read it for free. I have a Scangauge II from back in the day, they still sell them for around $150 apparently, you would think they would have come down in price sometime in the last decade...

After 12+ years, just consider a new traction battery as a normal maintenance item.

 

If you want a link to the thread I have on the battery reconditioning topic, below is it :

2010 Prius II HV Battery Reconditioning

Happy reading .

Good luck and keep us posted .

 

You said you shouldn't ever go into Purple zone but then you list a bunch of scenarios where it's perfectly normal for an older battery to go into the Purple zone.

 

Checking and servicing-replacing the the bus bars can certainly help the hybrid battery efficiency - There are lots of threads covering it.

Here are the 3 signs that your hybrid battery is wearing out. At this point the 'Check hybrid system' or red triangle might come on with error code PA080.

1. The bars on the MFD showing the battery gauge will change not one by one in a few minutes, but more frequently. It could jump 1 or two bars up or down instantly depending on driving faster. A battery in OK health won't do that. This is what I would look out for if I were you.
2. You will notice a rougher change of power between the engine and the electric drive.
3. If you have a PA080 code, all your error lights will be on in the car.

 

The old rule of thumb was about 4 times a year. But it depends on your individual situation Twice a year is probably enough.

 

Further explained:
#1 is not the battery wearing out... It's simple sign of aging and time for maintenance/reconditioning
#2 never heard of this, unless of course you're referring to vehicle warning lights and systems shutdown
#3 something in the hybrid battery system has failed and subcodes have been stored to help you find out what that something is.

 

Umm, I list two, and actually they apply to a good battery too: 1) Going up a mountain, and 2) pulling a trailer with the A/C blasting. Neither of which would apply to "My '06 with 127k goes down to 2 purple bars all the time, usually in city driving."

That statement tells me his battery is due for replacement and the car will run better (and get better mileage) once it has been done.

The process takes about an hour for somebody with experience, so MIdasko doesn't have to worry about going several days without a car.

 

#1 is directly the result of the battery wearing out and losing capacity. A little charge or discharge makes large changes in battery voltage (battery capacity is measured in amp-hours, and horsepower * time = amp-hours * volts. The horsepower used/created during driving hasn't changed, only the amp-hours is less, so by that equation, that means the voltage has to have a bigger response, hence the bars on the MFD will change more).

#2 is apparently referring to when the gas engine kicks on and off, although in my case I didn't notice any change in roughness when the battery got old. That one could be aging of the engine and fuel line/pump.

#3 basically yes. In my case, only a few lights came on, and only the P0A80 code was active, but in some cases more lights and error codes can occur.

 

Maybe in the midwest where you live... But my main travel route is Seattle to SF Bay Area, which is North South between Western Cascades and coast range... When you climb up the Siskiyou pass you're going to spend a 1/2 hour climbing 4000 feet up a mountain and while there's lots of factors, it's pretty hard to make that drive without going into the purple. I think only once, right after reconditioning the pack, out of 60-70 times have I made it over that mountain without going into the Purple.

 

Doing some more research (such as this thread), it appears the MFD battery bar display uses "coulomb counting", not voltage level to determine state-of-charge (SOC). I'm not really sure how that works when the battery gets weaker and has fewer coulombs available. Seems that the limits of 80% and 40% SOC for the battery display might get stretched, and this would weaken the battery further?

Anyway, I'm happy that I'm just now looking at this after 13 years of owning my Prius.

 

Toyota Stealerships bill 6 hours for battery pack replacement... 18 minutes is my record for pulling a pack and having it all stripped down and ready for testing, so I'm fast, but the one time I did install a new pack it took 2.25 hours and with practice I could maybe go below 2 hours, but 1 hour, no way! At that speed it's way too easy to make a mistake or overlook something.