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How To Understand Toyota Prius Battery Health Using Dr. Prius App

The folks that developed the Dr. Prius app are heros. They have successfully given us Toyota Prius owners a tool that we can use to check battery health and see if it is ready to fail. This is great, but for the someone who knows almost nothing about their Prius, it can be confusing. Here are some helpful hints that will allow you to know if your Prius traction battery is having issues.


In full disclosure, I am learning about how the software calculates and interprets the data that is shown on the Dr. Prius app. I will be sharing with you my current knowledge and why it is beneficial to you. I am not going to do a deep dive into this right now.

I want people to be able to seek help before their battery totally goes down and they are stuck with a huge bill.

Toyota Prius Traction Battery, Ni-MH Version

Nickel Metal Hydride (Ni-MH) is still used in some Prius models today. It is a very common battery amongst Prius vehicles and has quite a lot of supporting data behind it. This is what makes it such a good candidate to talk about, because it is everywhere and will be around for quite some time.

toyota prius hybrid battery

Nickel Metal has a characteristic, over time and through heat cycling it degrades. It loses capacity availability. To help you better understand this, think about a bucket that has water running into it. If the bucket gets filled and emptied regularly, silt and other debris can be left behind effectively reducing the amount of water that can be stored in the bucket. Ni-MH is the same way.

In order to restore the capacity we have to physically remove the "debris" to allow for it to once again be able to fill up completely, and the same is true of our hybrid traction batteries that have the Ni-MH chemistry. This means that we must have a way to "clean out" the junk, but no dealer will ever tell you that, they want to sell you a battery when yours has the infamous P0A80 battery degradation code.

So, what if there was a way to find out if our battery was on the fritz? There is and here is what you can do about it.

The Dr. Prius App And Carista Adaptor

In my previous story, I mention that the best $20 tool you can buy is the Carista bluetooth adaptor, and that is true. I have been using it to log information on my personal battery to see where I can improve it. I was astounded at how much information you can get for free from Dr. Prius. It tells you in real time all voltages and resistances for each of the 14 cell blocks in 2004-2015 Prius vehicles (this also will be true of Lexus CT just FYI).

When I started looking at all the voltage differences, I was not sure what they meant. There were differences from block to block and they all seemed to be shifting as the car drove, but other than giving me live data (which I knew how to read) I felt that consumers of this app could see data, but not know what it means. So, I asked a question.

The Dr Prius Logo

I emailed [email protected] and asked Jack what all my numbers meant. He told me things I already knew, but something I also did not. When it comes to resistance values, there is a threshold where if the value is met, it will trigger a master warning light and the car will not operate as efficiently as it could. This means you could save your battery before it goes down, using reconditioning equipment I will get to in another article.

The important takeaways when using the app is that you understand module voltages along with the resistance values that are given for each of the blocks. That is what I wanted to know and what Jack shared with me, what is resistance value will set a trouble code.

Here is the truth from the person who created Dr. Prius. He told me that while there is no minimum for internal resistance, the bars on the resistance values will turn yellow at 30 milli ohms and most likely set a trouble code P0A80. This is gold.

What Does This Mean For Prius Owners

If you are concerned about where your battery is in terms of life, Dr. Prius app is free. You will need an interface between your phone (or whatever device) and the car to be able to even see the data. I use the Carista, and so far I think it is worth the $20 I spent on it. In the free version, I can see all the data that is displayed in the headline picture and more importantly see what my internal resistance values are. This will allow me to then see if I need to be worried about my battery starting to fail. In my case, where I have 24 ~ 25 milli ohms of resistance, I should be aware that I am suffering a little bit, but not too much.

Carista Bluetooth Adaptor For Toyota Prius

My Prius has for sure been through some hard times, and when I built this battery, I had no clue if the modules were going to work or not. I knew they had 140,000 miles on them and the car drove fine before. I pulled them from the destroyed pack, put them in mine, conditioned them and drove the car. The only thing that has been of concern to me, is for the driving I do, I should be getting way better fuel economy, but I was not for some reason.

Once I learned this little hack about how to understand what the data was telling me, I began to figure a few things out. even though my pack was "okay" it could be better. My resistance values are not off the chart by any means, and I do not have any trouble codes, but could my pack be better? I think so.


As I gather data and do more research I will gladly share this with the community of people we have out there. For now, this is not a super technical article, and it is not designed to be. I wanted to tell you all be sure to check out my favorite 3rd gen accessory right now which is the Nimbus Phone Mount, found on Amazon.

Check out my other story Why the first generation Prius is better than either generation Nissan Leaf.

See you in the next story where I am discussing why Carista is the best $20 tool for your Toyota Prius.

Also Watch New tech means more MPG from your Toyota Prius and Click to Subscribe to Torque News Youtube Channel for Daily Toyota Prius and Automotive News.

Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He is an automotive technology instructor at Columbia Basin College. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter is also an Adjunct Instructor of automotive technology at Columbia Basin College. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter.


Thomas (not verified)    July 27, 2021 - 4:52PM

The green arrow from the electric motor logo to the battery quit and the car sounded different. I was on my way home from the red triangle coming up with a P0A80. I ordered a new battery for the code but am worried of the green arrow from motor to battery ,whichever part that is, failing. I'm short on money after the battery n am having trouble finding an article that addresses it. What probably failed and how much an I looking at? ty

Rick (not verified)    January 19, 2022 - 8:57PM

I have a 2004 prius when I was driving the red triangle appeared and started beeping then it got waitstaff the same would happen then the beeping was constant also showing a sign for door open I stopped driving it now I have to put charger on battery to start it has no notifications or beeping but the only way it will start is if I put charger on it for a couple of minutes the 12volt battery is only three months old I just had struts up front replaced is there any wiring up front that could have been damage help please.