[S Keith]

Originally Posted by Isaac Zachary

That's the rumor, yes, and I hope it's true. If I had my Prius fixed up more to the point the dying HV battery were the next step in fixing I'd try to get a Toyota battery. But I personally haven't heard of anyone who's been able to get one. But I don't know a lot of people looking for a Prius battery either.

It's not a rumor. I'm in weekly contact with my dealership. I collaborate with other builder in other regions, and they report the same.

Project Lithium does add a balancing circuit in each module. As long as the cells are balanced, the max and min voltages and currents of the Prius BMS do not go out of the range of the LiFePO4 cells. That's the beauty of LiFePO4 is that they charge up to full at 3.6V but can tolerate up to 4 just fine. 4V x 5 = 20 volts per block, which the Prius BMS will never let the battery reach.

Sounds like you're buying the hype. They are actually intolerant of > 3.65V. This increases the stress on cells. The reduction in charge voltage from 4.20V to 3.65V is a primary reason LFP has longer cycle life. Initial LFP specs identified the operating range from 2.0V to 4.2V. After a few years in the field, it was discovered that this was preventing them from reaching quoted cycle life and was reduced to 2.5V to 3.65V losing only about 5% of the total capacity.

There's no balancing between the modules, so while the 5S in a single module may stay reasonably well balanced, there's nothing preventing drift between modules.

I'm guessing you haven't spent dozens of hours working with Techstream. I've seen > 20V/block in techstream, particularly in cooler weather and regularly over 18.25V in all conditions.

NiMh SoC is both voltage, current and temperature dependent, i.e., it changes with temperature. LFP does not. When colder, the car will push the LFP to higher voltages than it will when hot.

They can also tolerate faster charging currents, which is why the LiFePO4 Teslas charge faster than the traditional Li-ion Teslas. But if there is no balance circuit then yes, the LiFePO4s will eventualy fry themselves in a Prius. I haven't heard of anyone having problems with the Project Lithium drop-in modules even with many now running them in their Toyota hybrids. But as you will surely agree, they haven't proven themselves yet like Toyota's own NiMH batteries have either, and won't be able to until some 15 years later, if they make it that long.

More hype. Gen4 NiMH modules (which are in all Gen2 packs) are rated for > 20C or 130A. Typical large cell EV rated LFP is 0.5C charge and 1C discharge. Yes, they can be designed for higher C rates, but the compromise is cycle life.

This was a sloppy and cheap implementation. The successful Lithium conversions go the extra steps to create a spoofing system to feed the battery computer the data it needs to have the car treat the LFP like it should needs to be.

I have extensive personal experience with NiMH and Lithium. I personally have >10kWh of LFP and 55kWh of Li-NMC and have done a lot of cell level testing. I've built an off-grid power system using the aforementioned Li-NMC for our eventual retirement home. I don't know everything, but I know what sound design approaches look like as well as bad ones.