Higher capacity battery mod?

has anyone here been using the nexcell?

 

I have not seen many, if at all. For a car like mine (250K, 2012, JDM engine just installed) it would not be cost effective at all to put in the NexCell battery since the old one still gets about 7-9mi in this March weather.

And before you read further, I am unlikely to actually do anything with the battery unless it ends up failing at some point in the future. The notes below are for future me, or anyone else who might find it useful.

I have done some poking around, and found this article by PushEVs. This suggests to me that the cells in the Gen 4 Prime are 25Ah.

• Toyota Gen 4 Prius PHEV (Prime) with 96 cells (96s1p): 96 x 25 Ah x 3.667 V = 8.8 kWh

The PIP has 56 cells (56s1p). Let's assume that the nominal voltage is 3.7V. Matching the formula above, we would have:

• Toyota Gen 3 Prius PHEV (PIP) with 56 cells (56s1p): 56 x __ Ah x 3.7 V = 4.4 kWh

Solving for __ we would get 21Ah per cell. This is within shooting distance of the Gen 4 Prime, and there are just more cells to achieve the greater range. I surmise that they are in fact the same cells, and the kWh have been calculated in slightly different ways for each generation.

In addition, used cells for sale on eBay are listed as working for years 2012-2022. Not that eBay is an authoritative source, but that would match what I have suggested.

Gen 5 Prime has 72 cells with 50Ah each, and it seems they are the same dimension as the Gen 4 according to the video that black_jmyntrn linked. So I THINK that getting my hands on a used set of 56 Gen 5 Prime cells would be the most reliable way to go.

Of course, those batteries are only a few years old so they are not cheap. If I was to go the Ali Express route I would think to do the following:

1. Buy one cell to check for physical fitment.
2. Test that cell at about a 8-10A charge current, which is about what it would see with a fast charging setup. I would monitor for temperature constantly during this. (The Ali Express item I see says it is good up to 100A constant charge current).
3. Test that cell for heat during discharge. The most current I have seen on my car is 200A peak, so I would have to rig up a setup to discharge at this rate. (The item says it is good up to 200A constant discharge current).

I suspect that the cell would pass test 2 and 3 since it is within the advertised limits, but who can say for sure with Ali Express cells? If all three check out I would then:

1. Order 60 cells, and go through the charge and discharge tests with them to check for temperature.
2. Choose 56 of them and install them in my car.
3. Go to a fast charging station with the top of the battery off and use an infrared thermometer to monitor for temp spikes.
4. If all good then seal up battery.
5. Get a real time readout of some of the battery temp sensors, and monitor during real use until I felt that all was well.

Concerns about using the cheap Ali express cells would be that they may be fine for months or years, but then start to fail leading to being stranded after having gotten rid of the reliable Toyota cells.

 

Let me clear something up real quick: the video I posted wasn’t meant to say “go get those exact cells.” It was to visually show that the Gen 3, Gen 4, and Gen 5 cells are all the same size and form factor—which opens the door to some really interesting compatibility possibilities. That’s the part I wanted folks to pick up on.

So no—don’t run off and grab Gen 4 Prime cells just yet, buddy I’m not recommending people swap anything blindly. But I am trying to widen your peripheral here. The conversation shouldn't stop at “that’s not what Toyota intended.” We should be asking, “what else could work?”

Also, on the skepticism thing—you’re right, I say a lot of things that sound a little ahead of the curve. But that’s kind of the problem I have with how things work online these days. Far too many people won’t believe a new idea unless someone has already written a 10-page guide about it. But had I waited for someone else to do that before taking action, I wouldn’t be anywhere near the progress I’ve made today.

One last thing—can you confirm if you’re the same person I’ve been emailing with about this battery stuff? I want to make sure I’m not repeating myself between inboxes and forum threads.

Appreciate you being open-minded and thorough. That’s what keeps this space alive... the thing is, you are still narrow visioned and if I am right you are not from the USA, so I ask do you have any fully electric Toyota/Lexus vehicles where you are from? What about other PHEVs? .... widen your peripheral and don't stay stuck on the Prius cells is what I'm trying to get you to see...

you bring up valid concerns, but I’ve gotta push back on a few points.

For one, yes—any lithium cell without a BMS is asking for trouble. That’s not up for debate. But here’s the thing: the Prius Plug-in already has an integrated BMS. And unless someone’s doing a wild frankenstein job with their install, that system is still in play. So it’s not like folks are just tossing in cells and hoping for the best.

Now, your argument sounds great if we’re talking about throwing random eBay lithium packs into a lawnmower. But if someone is sourcing comparable high-grade cells, verifying specs, and matching capacity and discharge rates—then no, the idea isn’t automatically dead on arrival because of cost or safety.

And respectfully? The "buy a Tesla" comment kinda skips the point. This isn’t about EV purity or trying to turn a Prius into a Tesla. It’s about pushing the boundaries on what's possible with a platform that was intentionally designed to hide most of its capability from the end user.

We both know Toyota engineers are brilliant—but we also both know OEM decisions are driven just as much by cost, regulation, and long-term maintenance strategy. The fact that Toyota doesn’t advertise something doesn’t mean it’s unsafe. It might just not be in their interest to enable it.

I’m not saying everyone should run to AliExpress and grab 56 mystery cells. I am saying if you do your homework, run proper tests, and monitor everything along the way—there are smart, safe ways to level up the platform.

And for what it’s worth, some of the scariest failures I’ve seen didn’t come from Chinese cells—they came from people trusting “OEM forever” logic and ignoring degraded packs until it was too late.

 

As I said, that would not seem to gain me anything and I would go for Gen FIVE Prime cells.

I have not been emailing or messaging with you, and would love to have any information you can share with me. I AM in the USA, Southern Maine specifically. I am not pigeonholing myself into just Toyota cells, and would be happy to hear some suggestions from you. Though, to my knowledge you went with a NexCell upgrade?

 

Let me explain a simple thing that the safety of the car and the driver depends on. Anything that is designed for one car does not allow it to be simply transferred to another car without a certain risk to safety and an increase in the likelihood of damage during operation of the car.







Chinese statistics on electric vehicles. Every day in China, 8 electric vehicles catch fire. 3,000 per year!
These vehicles are made in China, equipped with Chinese batteries, which are made at production sites and tested before being installed in the vehicle.
Over 3,000 EVs Fires per Year in China, Insurance Premiums Leap 20% - EnergyTrend

Note that the batteries installed in electric vehicles are relatively high-quality and have passed the test, while the defective ones are sent to trading platforms for use by electronic hobbyists.
But when scientific approaches are ignored, safety is of no concern, and the priority is to make a profit, the result is obvious.
For example, Tesla has had just over 230 fires in its entire history since 2013.
Every day in China, 8 electric vehicles made in China catch fire. 3,000 per year!

Now to the questions about using other modules in a vehicle that was designed for specific modules.
All BMS are designed for specific electrical parameters, current, voltage, internal resistance, capacity, and type of chemical reactions inside the module. These BMS are designed with a certain reserve that ensures operational safety during operation, takes into account a possible set of unfavorable factors that can affect the thermal runaway of the battery. The cooling system of specific modules is also taken into account, the designers decide on air or liquid cooling of the modules, the number of cooling elements, methods for monitoring the temperature of individual modules and the overall temperature of the battery, a limit is set on the maximum currents, voltage and capacity / power that can be used without damage to a specific module. All this is calculated and checked repeatedly by engineers at the production site.

Replacing and installing another module from another car or purchased on a trading platform without carrying out work on designing another BMS, designing a cooling system, monitoring critical battery parameters, module temperature, their voltage, passing current and battery power is a very high risk that an emergency will occur.

When an electric vehicle battery uses DC fast charging under an ultra-low temperature environment, if the electronic control system fails to preheat the battery, the battery is at risk of fire. Another cause of the fire is lithium carbonate precipitation and the formation of lithium dendrites in ternary lithium batteries and lithium iron phosphate batteries. The addition of relatively cheap electric cells fleets also represents an additional risk due to high usage and more fast charging.

Lithium cells have a feature. They cannot be extinguished! One that catches fire will ignite another, and so on. A chain reaction will occur. What happens to your car in this case?

A smart person will not risk his car for a dozen extra miles or a slight increase in MPG.
There are safer ways to do this - hypermiling, etc.

 

Let me repeat this clearly—don’t limit yourself to just Prius cells.

If you go back and really look at what I’ve shared, I’ve been dropping gems throughout. The real key to successfully upgrading a PHEV battery lies in matching battery chemistry—not just sticking with OEM labels.

You may have missed the post where I gave up the goose on the battery I’m planning to use to build the next monster. Back when I thought one row from a 2013 PHEV pack (out of the four) would be enough to power a Gen 2, I went as far as making a full plug-and-play harness—only to hit a wall when I started learning how much voltage matters with these Prius and their batteries through the generations. That unknown piece of the puzzle taught me a ton.

Now here’s the thing: your biggest obstacle won’t be the cells themselves—it’s the terminal positioning relative to the ECU if your new cells don’t match the OEM dimensions. But if you’re like me, and you’re comfortable building a custom harness or know a guy and can send measurements to have a machined cable made after mounting the cells safely, then guess what? You can use nearly any cell that matches your target chemistry and voltage.

That’s why I keep saying: don’t box yourself in. The newer Priuses didn’t reinvent the wheel—they just stacked more cells. You're trying to keep the same count but raise the capacity per cell. And when you’re already down to do the work of making a custom harness, form factor becomes a non-issue.

So yeah—NexCell is what I used, but it’s not the only way forward. Not even close. Trust me when I say, the owner has a great mind and highly enthusiastic about my dreams and how ill get there one way or another.

I’ve got more I can share—just being real, I tend to move a little slower with new folks in my circle. Past experiences have taught me that some people are quick to flip the script or discredit everything once their feelings get involved. So if I’m not as open right away as I might’ve been years ago, I apologize. It’s not personal—it’s just that things have gotten a little salty around here over time.

 

my guy… I’ve gotta say, that post is giving some strong “I’m scared so you should be too” energy.

Look, it’s one thing to want folks to be cautious. That’s totally fair. But using fiery car crash images and worst-case Chinese EV stats to discourage creativity? That’s not it, chief. Projecting your fear onto others and calling it "wisdom" doesn’t push the platform forward—it just holds it back.

And sadly, that’s become the internet’s favorite pastime: shoot down the builder instead of supporting the build. Be a Debbie Downer with a loud forum voice instead of someone who says, “Yo, here’s how to do that safely so you don’t blow yourself up.”

You clearly know your stuff—so why not use that knowledge to guide instead of gatekeep?

This mindset right here is exactly why innovation in this space has been stagnant. Too many “nay-sayers,” not enough “why-not-ers.” Y’all tried to cancel me more than once, and yet… here I am, still building, still testing, still innovating. Unshaken. Unbothered. Unstoppable.

The fact is, pushing limits safely is how progress happens. And discouraging others because you don’t want to take that journey? That’s the real risk.

 

@mudder curious on your thoughts on this thread here. If an amateur wanted to double or triple the capacity of their PIP, what advise would you give them from a safety standpoint considering that mods like this are just replacing lithium with lithium or adding more lithium batteries to what is already there stock. Would the stock BMS system be okay in this case?

 

adding more wont work... you have to have the same number of cells just larger capacity... also... from what i hear... mudder and the product he made is having... issues... by my book until he's done work on a Prius, his knowledge shoudl always be questioned.