Prius Battery Replacement (GenII) Like you've never seen - NEW Cylindrical Cells

Great news everybody! We have developed NEW battery cells for the Toyota Prius. Not junkyard cells, not rebalanced cells, not new as of the year 2012 that have since sat on a shelf discharging, but brand spanking new, just produced, and they are both functionally equivalent and mechanically equivalent.

This is exciting on many fronts because now you can actually rebuild your battery and not just try to get a few extra months out of it.

These cells are produced in China by a company I have used many times to make custom batteries for my products. Everything from NiCad, to NiMH, to various types of Lithium. These cells have the same Wh capacity as the brand new Panasonic cells by Toyota. Take a look at this:



First thing you may notice is that there are only 14 of these cells, not the 28 as standard in the GenII Prius. This is INTENTIONAL! Why have 2 smaller modules put in series and only monitored in voltage pairs making a probable case for failure more than twice as likely once you add up on the possible failure mechanisms? It makes much more sense to have 1 BIG module. Less likely to leak, less likely to become unbalanced due to manufacturing discrepancies, etc.

This is produced as a kit. The battery cells are custom manufactured to be the correct size. There are plastic pieces that are custom manufactured for the end caps as well as to separate the cells themselves and to line them up during install. Having pulled apart and put back together OE Toyota packs many times, I can tell you these are 100 times easier at least to assemble into a pack. It's like LEGOs, everything just fits, exactly the way it should be engineered. Custom cables are also included to replace the bus-bars and orange cabling that go from the batteries to the HV ECU and to the main connection point to the battery. It is all drop-in-replaceable. Custom plastic shields to protect the batteries. The original thermal sensors mount on these batteries just like the normal cells. There are NO vent holes like the original cells. Also comes with new bus-bar nuts to attach to the battery terminals. Instead of two 7.2 volt 6.5Ah Panasonic cells, you get one 14.4 volt 6.5Ah cells. The math means the original cells are 46.8Wh and the new cells are 93.6Wh, which means they are equivalent when you build the entire pack since you use half as many of the larger cells.

Each cell is serialized custom. In the factory as they are produced, they are tested and packed into blocks of 14. Each of these 14 are then numbered 01 through 14 and when you install, you do the same and put them in the pack in order from 01 through 14. Can't get any easier. As we know the root cause for a failing pack is 1 of the 28 modules failing by getting out of spec a little bit from the others. By putting them all together, and having them manufactured at the same time and paired, the probability of this happening in the future is slightly less. It will still happen. These will eventually fail. But I would guesstimate an approximate life equal to or slightly greater than the OE cells.

These are the unmarked version of the cells, final ones for sale may have a different colour heat jacket. While aftermarket, these cells are superior and should last just as long as OE packs. Final market price is looking to be roughly $2000 USD for the kit, you do the install work yourself.

I'm looking for a few people willing to test it out and give your experiences for a couple hundred dollars off.

For those that are interested in some details, you can keep looking below for how an install goes.

Things are packaged in such a way that it is easy to accomplish the battery swap. The 4 similarly sized boxes on the left contain the 14 modules, the 2 larger boxes on the right contain all the custom hardware. In the future it may be one large box, but I don't want it to be too heavy to lift. Once delivered to your porch, you should be able to open it and carry each smaller box inside without effort. Not like the few hundred pounds the battery pack itself is.




This is the battery pack we have all grown to love in our Prii.



And from another angle:



And here it is without its turtle shell:



As you can see from the image above, 28 modules. This is a stock pack that has been rebuilt once prior. After rebuilding the pack using cells from late model low mileage vehicles, all 28 were replaced, that's when I was convinced there had to be a better way. Why haven't any of the engineers on PriusChat or elsewhere taken the time to make a new battery pack. Well, now there is one.

This is the non-battery equipment you will get in the kit. On the left are somewhat optional safety covers. These snap over the exposed bus bars hiding the exposed cell connects. The second from the left, long orange piece with holes in it like swiss cheese is basically an alignment piece of plastic. It keeps the cells in position and gives a channel to route the cabling. Looking at the 5 items clustered on the right of the image below, the top left is the new wiring harness. Now that you have half the cells, the connections between them are different and simpler. That is the wire. You can see the ECU connector head on it as well from this angle. Second small bag ontop right are the screws that hold the cells to the OE metal frame that Toyota designed so very well. You will only need half the number of screws. Someone needs to calculate the impossibly small amount of fuel savings there! Then the three small remaining bags from left to right are the temperature sensor battery clips, the brand new bus bars, and the nuts to attach the bus-bars and wiring to the cells. Straightforwards, right?!



Closeup of the battery clips to hold the thermal sensors:



Closeup of the battery bus bars



Closeup of the nuts and bolts





The cells come wrapped and packaged individually. Very secure to prevent damage:



One battery module per bubble wrapped blob



14 blobs, 14 batteries.



And a closeup of the modules:






Notice the plastic that separates the cylindrical cells themselves as well as the end caps. Something to also look at in the above photos are the slots and tab son the plastic pieces. The original Toyota cells use a system of bumps and depressions to make aligning the cells "easier" and keep them locked into place. I think this is superior and much much easier. The two tabs that stick out on once side of the cell fit perfectly into the two slots on the next cell. There are 5 separate tab and slot mates per cell per side. Also note how there is air gap between the cells. Notice how many cells fail in the middle of the pack where they get hot and have nowhere to put their heat. These have air all around them and the same stock cooling fan should work MUCH better at actually creating airflow.

Notice the serial numbers on each battery, the "dash number number" like "-01", "-02", "-03", etc








Here they are pushed together (not secured) and you can see the original for reference. The design is very good, you can see the plastic feet where they will screw into the Toyota bottom.



So put the alignment piece on, a pair at a time. Bus bar over the cells, wire on the cell, nut ontop. If you look at the image below on the wire, you will see that the heatshrink is labeled as "8-4" and "8-5". These are in order from "8-1" all the way up, and each wire goes on each pair of modules.



From this angle you can see the tab cutouts in the plastic piece that the cable wrap slides into. It is meant to be a snug fit, and it is.The wiring aligns just as it should.



Now with the old pack...



Remove all the old modules. Everything just unscrews



As you can see my OE Panasonic cells had a HV leak. That's battery acid. You're compressing the crap out of these modules and you're screwing right into the bottom. You see lots of cars like this. With the cells we are using, you are not doing that. I would be surprised if these leak like that at all. And the cylindrical shape of the cell means that it can contain much higher pressure without having a problem. Yay round things!



Now remove the OE cabling, you don't need it anymore.





At this point I took a break for the evening. Time to rip apart the car and get to this point was roughly 2 hours. Since this is high voltage DC, always label for other people.



Finished up the next day in a couple hours. Now take all the cells and move to the original Toyota Tray.











And then inside the shell. Everything works just fine bolting together, it is meant to be a drop in replacement and it is.







Then mount the original temperature sensors on the 3 plastic clips that came with it like so



And you can clip those under the cells. The position is just like the original. The HV ECU requires no special programming or fake outs.

Here is the wiring closeup in the channels of the almost complete pack







You can see above how the cable conduits snap right into place. All the wiring is tight and clean as well as numbered for easy access.

Then you can start putting the covers on. You don't really need these, but Toyota covered theirs with the orange bus bar plastic, so why not.





Old vs. New HV ECU connector. 1 to 1 match.



Start screwing in the batteries from the bottom. Only ever other hole is used because we have half the batteries!



Closeup of the connectors on the other side.



And how everything fits through the OE shaping. Like it is supposed to be there. At this point you connect the last 8-1 connector which makes the end point live



And the plastic protective covers



And here it is almost finished



Looking into the plastic void, what it protects





Top finished off nicely, bars attached, everything fits in stock equipment



And the final pack minus connecting the HV ECU connector



Ask away with any questions. Available now if you want to try. Right now, no warranty.

I've had mine installed for over 2 months now. It feels and acts like a brand new car. For less money than a "new sitting on shelf" pack from Toyota, my Prius is now like-new and should last another decade.

 

No. They perform just like stock by design. You would never know. And without opening the battery cover, nobody else would notice either. Even to a Toyota tech it acts and responds exactly the same.

Very slightly lighter. Less plastic, less screws, but the heavy part is the battery and metal. Metal is your original, so no change. Batteries are roughly the same in a 2:1 comparison.

Yes, actually lower. Since they're larger cells, it's lower resistance in general. Then with the two in series comparison it is still lower. Over time, it will also remain lower as the internal connections will not corrode or oxidize like the outside connections.

This exact kit, no. Gen2 specific. But the cells have no problems in Gen1 or Gen3. There is a specific kit for the Gen3 that's slightly different and produced. It has been installed in two of the factory owners' vehicles in China that are Gen3. I do not have a Gen3 personally, but it works too. Gen1 should work but more DIY will be needed, I don't think the market is strong to make something specific.

There were numerous tests done with the Prius when converting to a Plug-in was all the rage a decade ago. The conclusion was and still is that any more battery is a waste. Keep in mind many Prii are driving around with 50% or 20% of original capacity in their packs and barely even notice it. Only on very long descents will you notice that until the pack starts to fail. Having air around the pack also should keep in cooler so technically "more performant" but really that wasn't the goal.

I was an am tired of all the posts about how the battery went bad, people spent $2k on a refurbished pack off eBay and it goes bad in months because the cells are also 10 years old. Or the people getting new $4k packs installed at the stealership and the date code says they were made years ago and only have a year warranty (although that might have very very recently changed?). This is not for the cheapskate that wants to spend $30 on a cell on eBay and play whack-a-mole replacing cells in perpetuity. This is for the person who wants a new battery which until now was impossible without rolling your own solution.

 

That is good to hear for people that go to the dealership. What kind of warranty did they give you? And just to confirm, you opened up the battery cover and read the date codes off the Panasonics?

 

Doubtful. I am merely a spec of dirt on their billion dollar shoes. I make some products to make money and some products because I just think the project is cool and fun. This is a cool and fun project. Cost less than $40K and hopefully the community can benefit.

 

That is a great point, and one that should be considered.

Not quite. This has been modified. The plastic kits are slightly different, and the battery cells themselves are different. You cannot buy these from anywhere else at the moment, but you can buy a look-alike. That's why I will change the final look. Used the base design as a leap-pad for these.

As you mention when the Chinese say "6.5Ah" capacity, they really mean "maybe 3Ah capacity" and that's exactly what's in those other cells you can buy on eBay and Ali-whatever.

Just for some background, I have access to the same battery testing tools that are used to test packs from the big auto-manufacturers. Meaning the company I work for actually produces the silicon that goes inside of many BMS systems which are then sold to car brands like Toyota as a hypothetical example but brands you have a dealership for in your area. So I am not just some schmuck off the street selling stuff, I have put these through extensive testing outside of the car for many months after the final batteries were locked down.

Eventually there may be a warranty. This isn't my first business rodeo. Got 7 going at the moment. This was just a fun venture that may make 8 if there is any interest. Otherwise, it is just an expensive fun toy project.

Shipping would be inclusive to the lower 48. Luckily NiMH doesn't have the same restrictions as Li batteries right now, so shipping is really just freight as I am sure you are aware. I think there are some advantages to this design over the stock pack, and price may drop with volume over time. Initial price offering is just that.

 

These cells have been tested extensively and are not off-the-shelf.

 

I had it custom made lol.

 

Very similar plastic kit, some dimensional differences and accuracy improvements. Batteries themselves are different. These D-cells are made specially and assembled differently. Just because things look similar, doesn't mean they are.

I bought one of those kits when they came out a few years ago and played with them. My testing showed less than 3Ah capacity per cell. The plastic pieces that came with it did not fit properly.