Prius Batteries

Hi Folks,

I have a 2006 Toyota Prius with-- get this-- 240k on it. I’ve had hardly any repairs to it.

I know that eventually the battery pack is going to start to go. But, what I’m wondering is, what is the first indication, and is there a warning other than outright failure. What happens in that case to the operability of the vehicle?


You may want to go to a Prius forum for this, lots more folks there that might know (Priuschat is one, I think). It’s fairly rare, so here’s hoping you don’t find out!

You also might want to read this, about a Camry hybrid owner who figured out his ‘bad battery’ was actually just some corrosion in the connections:

If your driving habits and patterns don’t change you’ll notice a decline in mileage as the ICE runs more to compensate for a weak or failing battery.

Those batteries are lasting longer than they had originally anticipated, and the long term operating costs of these cars are quite low. I have a customer with an 04 Prius, still has the original brakes.

At 25K miles/year (mostly highway?) your hybrid battery may not have been used much. The perfect scenario for long life. Drive on…

The battery will throw a code and a big red Triangle will appear on the dash if the battery has a failure. also, the torque would be reduced since the car would depend more on the gas engine. Lower MPG is not a good way to detect battery failure since it could be many other reasons for the lower gas mileage like low tire pressure, clogged injectors, bad pcv, old spark plugs, etc. If you can rule out all normal car problems that can cause lower gas mileage, then I might start checking the 12V battery(not the traction battery). The 12V battery can cause lots of weird failures on this car while it is dying.

One of my battery modules failed in the traction battery. Dont drive it when it does. It overcharges the remaining good batteries. 1 of 28 modules failed and was fairly easy to replace. It is more work than most people have experience for and you will need to follow some high voltage safety practices. My 1 cell failed at 291k miles currently my 2005 Prius is over 300K, but only shows 299,999. It seems the battery failure is based more on time than mileage. If you can change a bad module by yourself it could cost you a little as $100 to get up an running again.

As for preventative maintenance, keep the battery cool and make sure the air conditioning works. Keep the battery vents on the right rear seats clean of debris.

These cars are low maintenance. My old 2008 that was wrecked had 150K on the original brakes. The only major problems these cars have is the electric water pump. They fail around the 80K mark. The 2008 failed at 72K. The 2005 failed at 240K, but I didnt know the history of the pump replacement. I am on nearing the time to replace it again, but it would be a simple fix since I have done it 3x. Also the engine water pump failed at 280k miles. Other than the water pumps and 1 battery module, I have only changed the oil, coolant, transmission fluid, pcv valve and spark plugs. That is pretty reliable for a 10 year old car and 300K.

The link to the Camry story shows what the battery looks like.
This is my post on the battery replacement on PriusChat

Toyota is taking steps to decrease the longetivity of the Prius battery packs(I hear they are going to Li ion-should generate more complete failures{why screw with something that works?} If I could afford it,I think I would buy a prius.

This is all really interesting, folks. I appreciate the details responses, and have already checked out some of the links. MUCH appreciated. This car has really been something else… I roughly estimate I’ve saved at least 10k over the life of the vehicle to date, compared to the Subaru I was driving. And, nothing against Subaru per se, it’s more a statement about how Toyota seems to have just absolutely nailed the reliability of this particular generation of Prius’. Thanks again! Love this community. :slight_smile:

“Toyota is taking steps to decrease the longetivity of the Prius battery packs”

So the strategy of intentionally lowering product quality?
That worked so well for GM in the '70s & '80s…

Hopefully not,but sometimes unintended consequences will tip the scales in favor of the manu,the only reason I’m saying this is because of the experience I have had with these types of batteries,hopefully by now the Li ion is as reliable as the Nimh batteries( never heard of the metal hydride battery catching on fire either(I think it was a pleasant surprise when the older batteries held up so well-when they were no longer suited for a car they could go many more years as a solar storage unit.lets hope this type does as well,Toyotas reputation is on the line with this one,because I know so many happy Prius owners)

A problem with Li-ion (and lead-acid too) is that service life varies a lot with state-of-charge and charging patterns.
Li-ion cells don’t “like” to be kept full, yet the typical user of electronic “gadgets” top up the batteries as often as possible or even use the device while plugged in the charger & keeping the battery full.
After all it’s comforting to have a full battery available (just like a full tank of gas) “just in case”.
Usually there’s one sentence buried in the instruction manual that keeping the battery full can shorten its life.
I have some laptops at work approaching 10 years old with their original batteries.
I make sure the batteries are stored at 25-50% and don’t give out chargers to the students that borrow them.
Professors who were issued these same laptops and used them plugged in all the time got the typical 2-3 year battery life.

Lead-acid, of course, really “likes” to be kept full.
NiCd cells do best when stored long term empty or near empty.
With NiMH however it doesn’t really matter re service life if they spend most of their time near empty or full.
Just don’t over heat them, over discharge to cell reversal, or over charge, which makes heat and internal pressure.
The Prius keeps them 40-60% charged, which minimizes heating.

I’ll go slightly off topic . . .

We have a few 42V parallel hybrid GM trucks in our fleet

They’re programmed to keep the batteries at about 50% charge. The 42V battery pack actually consists of 3 12V batteries in series. I replaced the batteries on one truck last year. The batteries were 10 years old. It worked out to less than $500 for the 3 batteries . . . genuine GM batteries, made by panasonic. There are at least 2 other trucks of the same vintage, and they’ve still got the original batteries

Yeah, I know it’s not a hybrid like the Prius, but there are some similarities, and the batteries are both japanese

The hybrid cars have very good battery management systems, so I’d expect they’d do a lot better than people do.

That is very interesting,so the moral is"listen to the manus" thanks I will let my Li ion’s idle now(no wonder they didn’t last very long-do like the run time though)

Toyota has always planned on having lithium ion batteries in the Prius. When the first gen Prius came out lithium ion was not dependable enough. With recent advancements in technology Toyota is shifting toward lithium ion as it now believes it will meet reliability standards.