Is adding a second battery possible?

Id be very interested in your results. From my understanding there is a benefit but its around 10% better fuel economy and more peppyness. but I'm only going on Dr Prius Nextcell Lithium cell upgrades. What you have may be completly different with LTO. Something ive wondered about myself. Fluid cooling is also of interest and a huge challenge in itself!

Ah yes Ian Hooper of Zeva, i used to use a lot of his 8S BMS boards on various systems. Still use them! A shame he hung up his hat. But glad he opened sourced it all. I just don't have the time or fortitude at the moment to try and create his BMS from the source files.

Ah and Rodney Dilkes of EV power! yep i love those cell balancers! what a great solution they've been! only recently did i discover those cell balancers have a that 1 wire loop to turn things on/off if any cell goes into the danger zone! was great as a backup when my BMS failed.

But Rodney said to me just a few weeks ago, he wont sell me those Cell balancers for my Prius project as they are not designed to see100+ Volts... I wasn't aware that would be an issue.

That sounds like an interesting cell monitoring solution by that member. I certainly would be interested in it also. As there really isn't a great deal available out there without spending a lot of money. I'm looking at around $2000 with shipping with the Orion BMS2, and I'm on a wait list due to parts shortages :/

 

I should of hit reply instead so you would get an alert.

 

Hopefully I will see him tomorrow and tell him there is export market interest as well ..... maybe that will get him re-inspired to get back into the production stage.
The original set up used optic fibre links but issues with getting and keeping a good connection had him switch to single wire canbus instead. He is a very clever bloke, unfortunately his talents are well sort after so big $$ jobs keep getting in the way as well

Nearly finished pack 3, broke a terminal off in one of the cells getting a bit heavy handed tightening them, so 5 down now ..... these are pricey eggs I'm breaking to make this omelette :lol:

T1 Terry

 

Hopefully you had some luck re-inspiring your friend. And yes Optic fibre would be no good for a car in my book. I have enough trouble in my job with optic fibre issues!

Bugger, yes, LTO are not cheap! Something I've not been able to find solid information on is how LTO compares to NIMH with energy density?

 

Energy density is a bit like Ah and Puekert factor and charging efficiency, it doesn't tell the full story and is really just a number resulting from basic maths with half the equation missing.
The real measurement should be something like "full load watts per kg", so the voltage drop under load is added to the equation along with internal resistance causing losses to heat and chemical reactions and then the return cycle losses till the same full capacity is reached.
The module pair might have a nom. voltage of say 14v, but under load that drops to less than 12v but goes as high as 18v when recharging. Those are the numbers that really should be used when multiplying the load amps and recharge amps. A battery built from cells that neither drop their voltage under load or suffer voltage rise when high rate recharging can provide a lot more energy on the full cycle and that would give a far better indication of the weight penalty compared to the "usable" energy storage .... then you have to factor in the safety aspect and the cycle life

T1 Terry

 

Prius batteries are designed to work within specific systems. Mixing batteries from different sources or configurations could lead to issues with compatibility and balance. The batteries need to be matched in terms of charge state, age, and performance.

 

Did this ever get completed?

 

It has been done many times and was a failure everytime including commercial products that were equally poorly engineered.

The trick is to understand how a viable ev works and then try to add ten battery packs in the hatch with custom bms systems and hacked Toyota controls. Not rocket science but close for an unreliable retrofit that would end up costing the equivalent of three or four Tesla Model S Plaids.

Buy a used Tesla Model 3 instead.

 

Disguise a Tesla as a Prius.

 

That would be best honestly. Toyota body quality and build quality with Tesla drive. I’m down haha. Thankfully, I’m not really looking for any EV swaps specifically.

I’m just looking to add another battery to give it a boost of capacity and to keep it and it’s already programmed “ burn off All the power mode” (SOC over 75% on for longer and more offer. If it can be locked in that mode even for just longer the vehicle without a doubt, get better mileage and strain the old ICE less on acceleration.

I think this should be possible with modern tech and already elapsed the time that people have had these cars.

I just learned that the rav 4 2019 and up has a DOUBLE nimh pack. Looks like it maybe may be two Prius C packs put together roughly. They are side by side with two fans. Total voltage is 245 volts on the pack. PROMISING. Toyota clearly feels that two NIMHs are indeed viable contrary to all the negativity regarding double batteries. Let’s be patient and figure it out.

These cars deserve it, NOTHING is made like a gen 2 Prius anymore. If you disagree go find me a current production stock car with an all metal intake manifold and radiator. I’ll wait…

 

I'm not seeing much in the way of innovative ways that Toyota is using to incorporate the traction battery without sacrifices elsewhere. Although the 13.6 kwh battery in the Prius Prime is a significant increase over the 4.4 kwh battery of the Prius Plug-in, it's still not without significant sacrifices to space, and there's still no spare tire.

The Chevy Bolt had a 40 mile EV battery incorporated into what used to be called "the tunnel' running longitudinally along the floor of the car. I think future iterations of the Prius should look at something like lithium polymer batteries tucked into irregular spaces in the car, to increase the EV range, and free up space in the cargo area.

 

Sounds like:
I just found out that Charlotte from the next street has size 5 breasts! PROMISING!

So, your information is from an unreliable source.
There is one battery, not two. And not at all like in the Prius C, where the battery consists of 20 modules.

There are 34 modules here. 18 modules on one side and 16 modules on the other side. 34*7.2V=244.8V. All modules are connected in series, one circuit, one relay group. There are two fans because this is a feature of the layout and one fan will not reliably cover all the modules.

The battery and the layout of the modules and blocks are identical to the Lexus NX300, which was produced back in 2014.

The layout features of this battery are made in such a way as to install it in the car, observing the laws of car construction, for the best location of the centering, controllability and other parameters that are important for safe driving.
And of course, the operating parameters of the hybrid installation, which requires increased voltage, were taken into account.

Battery by MAX2 posted Mar 28, 2025 at 10:26 AM

 

Hey well thats why I asked! So a more knowledgeable person like yourself could enlighten the internet community for us all! It definitley looks like two batteries!

Regardless its really good to know we can get nearly brand new cells from these and similar packs for our old cars. Seems FAR more reliable than buying reman batteries.

 

Going back to about 4th grade, the teacher explained that a "battery" is a number of cells connected in series..

 

This link brings us back to pg 3 of this thread.
Is adding a second battery possible? | Page 3 | PriusChat

I wouldn't dare suggest anyone currently posting to this thread go back to pg 1 and read it.
That just wouldn't make any sense at all !

 

anything is possible. not everything is practical