So many of the batteries made today are lithium batteries of some sort, from mobile phones, laptops, and drones to electric cars and grid storage solutions. But this technology is relatively new; even as late as the 90s and early 00s the only widely-available batteries for things like power tools or the new hybrid vehicles coming on the market were nickel-metal hydride (NiMH). While it was good for the time, they don’t hold up to all of the advantages lithium has. There’s still plenty of hybrid vehicles on the road using these batteries, so if you’re driving an older Prius and want to give it a modern refresh, there’s a quick option to swap your old batteries.
Despite lithium technology being available for several decades, the switch to lithium for the Toyota Prius wasn’t instant, with many variants still using NiMH batteries as late as the 2020s largely because the NiMH batteries are less expensive and less maintenance-intensive than lithium batteries are. As these batteries lose capacity, the cars are still driveable but the advantages of the hybrid drivetrain won’t be as accessible anymore. The upgrade, from a company called Project Lithium, replaces these batteries with modern lithium technology that can improve the efficiency and performance of these cars even above their original capabilities since lithium batteries have more power density.
With the Toyota Prius being among the most reliable vehicles on the road thanks to the electric motor in the hybrid drivetrain taking a lot of stress off of the internal combustion engine, it’s often worth upgrading these old batteries to modern ones to squeeze every last mile from these workhorses as possible. With many of the replacement processes being almost as simple as lifting out an old battery and placing a new one in, it can be a no-brainer if that’s the only issue with the vehicle otherwise. This is also true of all-electric vehicles as well, although the process to replace the battery can be a little more involved.
Thanks to [JohnU] for the tip!
They’ve been sold out for years. Plus, its very clear that battery chemistry that goes above and beyond the stock capacity does essentially nothing without having hacked the Battery Management system (which hasn’t happened yet).
No, the batteries just fake the SOC status. The original NiMH batteries were kept within a narrow SOC range to maximize longevity. LiFePO4 batteries are happy with wider charge/discharge status, so they just… lie to the onboard BMS. This isn’t hard because the batteries themselves end up with a higher overall voltage at any given SOC. If you Google “prius state of charge manipulation” you’ll see details on it.
They also haven’t been “sold out for years” – they just arrive in fixed (relatively small) quantities and basically disappear immediately.
I was able to snag cell for a Prius C 2015 from their site. Installed it myself and saw immediate difference from the refurbished nimh cells prior.
Inb4 they burn people to death
>LiFePO4
Doesn’t charge below 0 C. It starts to plate the lithium on the electrodes, and that can lead to dendrites and breaking the separator, and then fire. LiFePO4 replacements for car starter batteries have nickel foil heating elements to warm them up in the cold, with the issue that it can take a long time, and the battery might not get charged at all if you drive short distances.
NiMH still charges down to -18 C or so. You just need to limit the rate to 1/10C. Flooded cell types may vent hydrogen when charged too fast in the cold, but otherwise they’ll survive.
It sounds like a simple solution to these problems is to warm the planet up a bit
On it!
It doesn’t appear that these lithium modules have battery heaters, and the prius itself didn’t historically come with one (newer plug-in priuses with lithium cells do). Unless I knew that the Prius BMS was already cautious about charging in cold temps, I’d definitely be concerned about installing this mod in climates where the battery might freeze.
But although it’s commonly stated that lithium batteries can’t be charged below 0 c, including by the manufacturers of said batteries, the reality is not quite as bad – if you’re limiting charging to 1/10 C as in your example, studies suggest most conventional lithium chemistries can handle -10 Celsius without any measurable lithium plating (and some propose that you can safely charge down to a temp of -20 or -30 celsius if you limit yourself to a paltry 0.02c. Why you would even bother at that point is another question).
[and yeah, I know, citation needed – I can’t find them right now, but there’s a lot of research into this not just for the sake of people driving EVs in cold climates but also because people want to use lithium batteries in satellites / mars rovers / etc]
“Unless I knew that the Prius BMS was already cautious about charging in cold temps,”
It is. It’s the same reason why the car only uses a fraction of the range overall – because Toyota’s main goal with the Prius was to make sure the batteries last as long as possible. It’s not a PHEV: it’s a hybrid. It gets its fuel economy mostly from a high-efficiency engine cycle. They’re ultra-panicky about using the battery.
All that being said: if you live in an area and park such that a car’s cabin is likely to get significantly below freezing, you should be taking precautions anyway if you want to maximize the life of everything. It’s not like the engine itself is some ultra-robust thing that’s super-happy down to cryogenics or something: you start the engine up at sub-freezing temps and do drives short enough that it can’t even heat up the cabin and the engine will wear, too. Yeah, low-weight oil will be low enough viscosity to *start* in the winter, but it’s not like the friggin’ car *likes* it.
I probably should’ve clarified by adding “in a way that’s demonstrably compatible with these lithium batteries” – I owned an ’07 Prius and I know it dialed back its charging of the battery when cold, but I don’t have any quantifiable info for either the Prius or these replacement batteries to say whether it’d still be done in a safe manner after the conversion.
I will say that the ’07 Prius was also not terribly smart about battery management at the high end of things – the battery pack cooling fan failed, and the car had no freaking clue. It was cheerfully boiling off a bit of the electrolyte in its cells for *years* any time it was driven in hot weather, and I had no obvious warning until the pack prematurely failed. I’m not too upset – I took the whole pack apart and swapped out the worst modules and it managed to hang in there until 180k miles or so – but I know it could’ve done much better.
Yeah, that’s why you should regularly use the Dr. Prius app (who are the guys selling these batteries, by the way), which reports pack temperature (and all the voltages, etc.).
It’s the same failing as any modern car has. They’ve got a ridiculous amount of information being fed into them and internal tests they run and they just hide all of it. I mean, it doesn’t matter to the car manufacturer: so long as the car lasts to its warranty, it’s a win for them.
“that’s demonstrably compatible with these lithium batteries”
You manage it yourself. That’s what I’m trying to say. How can you avoid it trying to charge the battery when cold? Don’t let it get cold. Problem solved.
If you say “but that’s not an option for some people!” well, then, they’re going to age it faster than normal. But people in those situations are aging their cars faster than normal anyway.
>you start the engine up at sub-freezing temps and do drives short enough that it can’t even heat up the cabin and the engine will wear, too.
That’s why cars in such climates come with engine oil sump heaters, that are used for 5-15 minutes before starting the car. It’s also enough time to use a small electric heat blower inside to melt the windows.
The irony is that in cold climates you do have electric outlets at nearly every parking spot, but these outlets aren’t wired or built for continuous use. The wire gauge is entirely too small, because they’re only ever meant to be used for a couple minutes at full power.
We just donated our 2002 Honda Insight to a local school; its need for batteries and some other maintenance put it out of “worth running” for us but its such a lovely car I’m glad someone will get some more joy from it.
While investigating possible options for it, we inquired into selling it to dealers and scrap vendors. They won’t touch them: cats and NiMH batteries are both far more trouble legally than anyone in those business wants to deal with, around here.
Even the VoTech school had to go through a month of approval seeking from higher powers, before they could say whether they could take the car.
Cats are definitely problematic, but I’m not sure if I’ve heard of them being legal trouble – did one knock over a priceless vase?
Shame to see another Insight taken off the road, especially if it was a manual. There were only 14,000 made total and it was the original hybrid supercar. It held the fuel economy record for 15 years. They are worth fixing to keep them running.
High-quality, new replacement HV batteries can be had with 3 year warranties for $2000. I know because I just had Greentec replace my original pack (2005 MY) with a 20% higher-capacity pack for about $2300 out the door (sales tax in my state is robbery). And that is in a CVT with 200,000 miles. Should be good for another 200k miles now. May have to replace the rubber bands in the CVT in the next 50k-100k miles…
You should have installed the LiBCM lithium battery into your Insight.
Sigh, I don’t see an BMS for each unit… lifepo4 is safe but still not that safe… Note yes the car BMS does check every other cell, but not on each cell.. so without proper BMS on Each cell I wouldn’t recommend this system.
Their FAQ does state it has a special ‘balancing circuit’. A quick skim of their page doesn’t have all the technical details I’d like, which frankly is fair enough – you put the work into make a product why opensource the whole lot and make it easy for your product to be knocked off in lower quality. But it sounds like it has everything you might need to make this is a simple drop in replacement except perhaps some active thermal management to improve the battery performance over a wider range of temperatures.
It might be snake oil, but it certainly looks and sounds reasonable.
There is no way to make this work from BMS standpoint. You need module to module balancing as well, so some way of communication between the modules which they lack.
Since the stock BMS is not monitoring the individual cell voltages, there is nothing stopping it from over-charging or over-discharging one of the series elements in the module. No internal electronics can protect for this.
Variable self discharge rate is the big issue when you have many cells like this in series, hit those cells with high power charge pulses especially in cold weather to get some of those dendrites forming which will make it worse. Once the dendrites cause the cell to short out and self discharge to zero, which means the rest in the module will now be over volted for the same module voltage, quick descent into rapid disassembly event.
Add in there random prismatic cell quality and pretty high charge and discharge power, this is asking for real trouble.
“from over-charging or over-discharging one of the series elements in the module.”
Sure there is: you spoof the SOC to keep significant headroom from fully charged/discharged. In a Prius this isn’t a huge deal anyway because it shuts off charging at a fairly low SOC.
If your modules are so far out of balance that you eat entirely into the headroom and one is “critically full” while the other hasn’t hit the max, you would’ve already thrown an error and prevented the system from turning on anyway *way* before that. That’s *why* it monitors delta-V between the modules – if it gets too big, it panics.
“when you have many cells like this”
It’s a freaking Prius, not a Tesla. It’s not that big a pack, the vehicle itself only uses a small fraction of the capacity, and gentle capacity decrease over time does nothing except slightly decrease the fuel efficiency.
I just purchased one of these NexPower Lithium batteries for my 2007 Toyota Prius and installed it last week (14 lithium modules instead of the 28 NiMh cells). The above picture must be of the version 1 lithium modules because the V2 cells I just received each have a circuit board inside that I can see through the vent holes on the upper covers (balancing circuit? Internal BMS?). Also, comparing to the above, the outside casing was redesigned for better airflow around the module. All in all, they look to be very high quality.
I’ll have to report back on the longevity of the battery pack because I just installed it last week.
My prior dead/dying NiMh pack had the 28 resting cell voltages ranging from 7.5v – 5.5v. Half the cells had 6.5v or less. So if the combination of the Prius BMS, and the internal lithium module balancers can keep a tighter voltage tolerance than this… My Prius and I will be happy.
You can’t draw currents separately from separate modules anyway once they’re fully assembled, so the best “module balancing” method is… replace the entire pack with new modules with equal capacity to begin with. I mean, after a *lot* of usage you could disassemble the pack and attempt to cycle modules individually to try to equalize the capacity overall. But that’s not something that the BMS could do anyway since it doesn’t have a way to separate the modules. This isn’t a NiMH/LiFePO4 difference, it’s just pack configuration.
If you really care about maximizing the life of a battery pack, it’s the same thing as a vehicle, it would need to be taken completely apart and periodically serviced. You can’t magically “design” it to live forever when it’s sitting under a carpet in the back seat of a passenger vehicle.
On a Prius II (2008), you cannot drive with a non-functional traction battery. When the traction battery is dying, first you get a series of alarms on the dashboard, then the maximum speed decreases slowly for a few weeks, then the maximum speed decreases abruptly to an unusable speed like 20 km/h for a short period, then it is impossible to start the combustion engine and the READY light remains off. This happened when the car had about 260,000 km.
In Switzerland, it is illegal to install non-original parts on a car intended to be driven on public roads. But I learned that Toyota was happy to sell any part of the car. So I bought a new original traction battery for CHF 2400, and with the help of one of my sons, we exchanged it by learning from Youtube videos. It took us a day to disassemble and return the old battery for recycling, and another day to reassemble everything with the new battery. It ran like a new car from the first press of the START button. The only annoying thing is that we lost the custom settings on the control and navigation computer because we didn’t quite understand the wiring to avoid this, it wasn’t explained well in the videos.
This car is still running well with now more than 350,000 km.
I have several concerns about the NexCell lithium module. Here’s a video I filmed while analyzing a module:
youtu.be/E3IJzbdC18g