Replacing all the modules with brand new batteries

I’m the original owner of a 2004 Prius that went 190K miles before the hybrid battery started to fail. About a year ago I had noticed that it was not acting normally and would charge and discharge faster than it used to. The performance also seemed off, but it was such a gradual change it wasn’t really that noticeable at the time. I suspected that I might have to do something with the hybrid battery, but it’s such an easy thing to put off until the dashboard lights up with just about all the warning lights. I did some research (mostly on PriusChat) and while module replacement seemed like a logical choice, it became apparent that it was probably a short term fix and would be more like a constant maintenance effort. Similar to when a headlight goes out, it’s recommended that you replace both bulbs because the other one is probably going to fail soon. I considered getting a reconditioned battery, but that seemed to be more about letting someone else play whack-a-mole for you. I briefly considered a new Toyota battery, but discounted that pretty quickly. I might have decided differently if I lived in an area with $2000 batteries (not counting core charge and not counting tax).

I ran across a discussion on PriusChat about an aftermarket option that used new batteries that had the same capacity as the original ones and cost a lot less than a new battery pack from Toyota. The downside was that I would have to take the battery apart to replace the modules, but I would have been doing that with the whack-a-mole option as well. It seemed that the early adopters were having good results, so I decided to take a chance and ordered the kit from NewPriusBatteries.com.

I didn’t need the car right away, so I took my time and spread the project out over a few hours for three weekends. I’m sure that I could have done it in one weekend, but wanted to take my time and make sure I did it right. It also gave me the opportunity to learn some more about the car and the electrical side of the hybrid system. The purpose for this posting isn’t to tell you how to do the installation, but rather some things that I learned and modifications that I made. If you buy the kit, you’ll get very detailed step by step instructions. One thing that helped me though is that when a step in the instructions had me removing bolts or nuts, I’d put that group into a ziplock bag and put a piece of paper inside with the step number. It seemed kind of anal retentive at the time, but it sure made it easier putting stuff back together again. I also took a lot of pictures and it occurred to me to take a picture with the loose bolts/nuts were they came out of the case. I did refer to those pictures one time. There are some threaded holes in the case that don’t have bolts, I assume they are used to hoist the battery pack into the car. They were the wrong size for the bolts that I had, but it helped ease my mind that I hadn’t missed something.

When you’re removing the modules in a Gen2 Prius, you need to be careful of the temperature sensors that are attached to the bottoms of Modules 1, 14, and 28. I wasn’t sure how they were held on, but the warnings in the instructions and from others on PriusChat were that they would clip right off, but to be careful not to break them. I was treating them like a Farberge Egg, but they aren’t quite as fragile as I feared. It might have helped to have seen one up close, so here you go. Kind of looks like a cobra ready to strike.



After getting the new modules in, you need to at some point put these temperature sensors back on the batteries. The kit comes with some clips for that, but I struggled for a while trying to figure them out. 2K1Toaster had a good picture of the clip and the sensor ready for installations. It makes perfect sense to me now, the problem I had was that I had the wires going out the wrong side. I was also nervous about damaging the sensor, but the leads on two of them were curved a little, which defied the installation. I straightened them out and they fit into the clips perfectly. Here is 2K1Toaster’s photo.



Before putting the sensors in place, I realized that the original flexconduit for the three sensors used to go through a plate in the lower part of the pack, but would now have to be rerouted to the upper area. I think that I tried a 3/8 in hole originally so that the flex conduit would fit nicely. Unfortunately I couldn’t get the sensors through that hole. I drilled it out to 1/2 inch and I could manipulate the sensors through. I think that it would have stayed in place, but just to be sure I put a ziptie around the flex conduit after it was through the hole.



Here are the new modules ready to be interconnected with the bus bars (new bus bars and nuts are included in the kit). In the foreground you can see a couple of clips like the ones on the temperature sensors, but without the sensor or the wires. These were also clipped to the bottom of some modules and were used to support the signal wires.

A friend of mine stopped by while I was working on the battery and commented that it looked like a bomb, hence the kitchen timer was added to complete the illusion.



Going back in time for a moment, here is my pack before disassembly to show you how the HV disconnect cables were originally routed (also notice how corroded the nuts are on the modules).



Because of the geometry of the new modules, and the fact that each one takes the place of two of the original modules, the HV disconnect cables can’t quite lay the same way as before. As someone else noted on here, the shorter of the two will reach the next module, but the longer one isn’t quite long enough to reach the one just past. Looks like it would, but it’s just a little too short. The solution is to either pull back the slack or arch the cables up some. I went with the arching method since it seemed like more work getting them pulled back into the ECU side of the pack. What I ended up looked like this.



Looks a little wonky, but once I got the module end covers on, I think it looked pretty good. The covers have cutouts in the top in case you need to route something in behind them. The 2nd module from the end was just in the right place. You can see it pushed up out of the way with the cables passing through. I wanted to take a picture of the routing, but was too lazy to disconnect the cables so I just moved the cover aside.

You can also see some 2x4s that I put under the pack. They were left over from another project and worked well to support the battery pack frame off the table. I don’t think 2x4s alone would be stable at all, but what I had were a couple that were tied together to form a tee. The instructions said to carefully hang one edge off the end of the table, but I liked this way better. I could keep the frame elevated and could reach the bolts on the bottom that held the old modules in place, and put in the new module bolts that were included in the kit.

Here it is with the covers all in place.



…and a close up. Looks intentional doesn’t it.



That’s all I have. I don’t have many miles yet on the car since the new batteries were installed, but so far it is running quite well. I’ll keep the group posted on the performance, but so far I am quite pleased. For expert advise you should definitely look elsewhere, but if someone has any questions about my experience, I’d be glad to answer them.

 

Thank you for the well wishes, but I don't think it was necessarily the geometry of the Honda batteries that caused them to fail, but rather what was inside of them. I see a lot of advantages to the cylindrical shape, primarily better cooling and containing the pressure when charging. There are some advantages to the Panasonic batteries and they were state of the art at the time, but buying replacement Panasonic modules isn't an option.

You sound a lot like everyone back in 2004 who said that I was making a mistake buying a Prius, that it was just a fad and that I'd be replacing the batteries every other year. 16 years and 190K miles later, this car has outlasted any of my previous cars. Based on gas savings alone, I know that having this car has saved me about $7500. Normally I might think that it's been a good run and get rid of the car, but seeing people getting well into the 200s and some exceeding 300K miles, I'm just a little bit curious as to how long I can keep it going. I definitely didn't want to spend too much time balancing batteries and trying to get a little extra life by exercising them, so I decided to replace the modules with new ones. Time will tell, but from what I've heard from others and what I've experienced so far, these new replacement modules are a great option.

 

I took a chance when I bought my Prius in 2004 while everyone was saying that it was a mistake. I was intrigued by the engineering and the potential for it to be a good alternative to a purely ICE car. Everyone was saying that I shouldn't get such a complex car when there was nothing wrong with a "normal" car. I did it anyway, and I'm glad that I did. Ends up that it is a superior car, and their fears and warnings were all unfounded.

I admit that I'm taking chance trying something new again, but I'm not one to stick with an old design, just because it's been around for a long time. As I had said before, if I could have bought a new Toyota pack or individual Panasonic modules for a reasonable price, I might have gone that route, but that wasn't an option for me. I'm going to give these new modules a try. I might not get 16 years out of them, but I have a feeling that they will do much better than a reconditioned pack. We'll just have to wait and see.

What I can say is that the car is running really well and acts more like it used to.