NexPower NexCell LiFePo Battery Upgrade

Nexcell pack is LiFePO4 Lithium Ion chemistry. They are not really more expensive than LiMnCO (like Tesla cells). This type does weigh more because of the Iron (Fe) used in them.

The trick was to integrate a Battery Management System that would make it useable for the Prius.

I wouldn't be concerned that your battery modules are not as advertised. They will probably last a very long time. Extreme heat may be one downfall of LiFePO4 chemistry compared to others, but it would take a lot.

 

As far as I can see, the manufacturer and retailer do not provide any information relevant to expected life of this product when installed as recommended (as a replacement for a NiMH traction battery). LiFePO4 batteries can have an excellent cycle life (>1000 cycles to 20% SOC) and calendar life (~10 years), but this requires a charging profile and usage conditions suited to LiFePO4.

From what I see, the testing has been relevant to safety (under conditions specified by CE, IEC, UN38.3), which tells us almost nothing about longevity (cycle or calendar life) when installed in a Toyota HV.

The charge test seems to use a controlled current and voltage power pack. Is that the way the Toyota HV works? To my knowledge, it is not. I think the Toyota HV will supply current according to the resistance of the battery pack, up to whatever limits are inherent in the Toyota generator, HV converter and charge control circuits. At low SOC, this will be a lot more than 5A. I have seen it deliver more than 130A in routine charging of NiMH. LiFePO4 charging is very efficient, but not 100% efficient, and the inefficiency results in heating. What temperature might be reached inside the LiFePO4 cell within a car traction battery under the repeated charge and discharge cycles of prolonged urban driving? Will an air-cooling system programmed for more heat-tolerant NiMH prevent temperatures that reduce life of LiFePO4?

If the capacity is 14*6.5Ah=91Ah, why does the advertising say ‘Nexcell lithium battery delivers 260Amp peak power’. That would be 2.9C. Is the battery rated for 2.9C during discharge? If not, this high rate would be bad for LiFePO4 battery life. Is the Toyota NiMH HV system rated for the peak discharge and charge currents expected from a LiFePO4 traction battery? If not, it is probably bad for life of the car HV system.

Does the suggested installation use all of the Toyota HV battery temperature sensors? Does the Toyota NiMH charge control algorithm use this temperature information in a way optimal for LiFePO4? Does the Toyota NiMH charge profile suit LiFePO4? How is charge termination accomplished? Could it keep charging beyond 0.02C? Could charge current ever exceed 1C? Could battery temperature ever exceed 40ºC? Could charging ever occur below 0ºC? Any of these would be bad for LiFePO4 battery life.

A good LiFePO4 battery BMS (=PCM) can be designed to shut down charge or discharge under unsafe conditions, but (a) these conditions should be specified to potential users; and (b) this shut-down is a good last line of defense, it still needs to be combined with a charging system that is designed for charging profiles that suit LiFePO4 (which are different from those designed for NiMH).

Personally I am a fan of LiFePO4 technology for use in cars, but it is very important for a seller to provide specs relevant to longevity as well as safety in the recommended use. Otherwise, let the buyer beware. Provision of convincing specs may require some performance of tests in a car, but much can be deduced from published scientific testing of LiFePO4. Ten years is a long time to wait for experience about longevity from enthusiastic early adopters.

 

Does that need a recheck? The battery is a series arrangement, isn't it?

 

ChapmanF, I don't know the answer. Do you mean it could only be a 6.5 Ah battery? That would be the same as my rav4 hybrid (NiMH), so you may well be correct. In that case "260Amp peak power" would be 40C during discharge and the above questions can be adjusted accordingly. I think they would become more problematic for the advertiser, as I am not aware of any other reputable LiFePO4 supplier who specifies that their battery is rated for 40C during discharge. Of course Amps measure current, not power; so maybe the advertiser has a voltage other than the battery voltage in mind. This would need to be specified for the "260Amp peak power" claim to be meaningful. It would also be good to specify whether the BMS manages cell balancing; and if so how.

 

There's another thread somewhere, where I asked the seller about the "260 amp" part, in particular because they reuse the service plug assembly that came with the car, which includes a 125 amp fuse. So clearly they're not expecting anything like 260 amps to happen in real life, for anything more than brief instants that are over before the fuse reacts.

Even the rated fuse current represents 20C for the original NiMH battery, which is also rated 6.5 Ah. I'm not sure you even see NiMH products being advertised for a 20C charge rate (maybe I'm mistaken); I think the key is those rates are never sustained very long.

 

Some batteries designed for special purposes (like RC aircraft) can have very high C ratings. "Often there are two C-Ratings printed on one battery – e.g. 45 / 80 C. The first specification (45 C) describes the so-called continuous current, which the battery can deliver permanently without being damaged. The second value (80 C) describes the maximum peak current that should be drawn from the battery." (https://www.drone-zone.de/battery-guide-what-does-the-c-rating-of-lipo-batteries-stand-for/). There must be a trade-off in things like price and longevity, but no doubt the specialist users understand those factors.

Here is a (1 second interval) log from my rav4 hybrid. Everything except engine rpm is on the right Y axis. Hybrid battery current (dark blue) does move around quickly, and it varies between approx +/- 130 Amps (with HB SOC from 42-70%). Cooling is shown elsewhere. I guess Toyota spent some serious research effort coming up with battery control and cooling algorithms that allowed their 10 year warranty on NiMH (and Lithium?) traction batteries; but we are not told those algorithms. I think they almost certainly must differ for NiMH and Lithium; in general a change from LA to NiMH or NiMH to LiFePO4 is not a 'drop in replacement'.



There are many threads on PriusChat about traction battery life, and it is a valid concern of hybrid car owners given the $ and environmental cost of traction batteries. It makes business sense for an intended long-term seller to give relevant specs to potential buyers. For 12v LiFePO4 batteries, examples of what I consider minimal and comprehensive specs from reputable companies are at:
https://www.renogy.com/content/RNG-BATT-LFP-12-170/LFP50100170-Manual.pdf and
https://www.power-sonic.com/wp-content/uploads/2020/07/PSL-12500-technical-specifications.pdf

The relevant details would be slightly different for a traction battery, but there is a lot of overlap.

 

Anyone with a track record of more than 3 years with one of these batteries?

 

Nope,
Generic Chinese LifePO4 have been used at diyelectriccar for about 20 years though in various “conversions”

My experience with the ones found in a Enginire Prius plug-in kit (different brand from what feels like millions of years ago) was meh as they were always out of balance and aged out before I got much use from them.

Like everything technology advances in 20 years

 

I have had one in mine for almost 2 years.
All is good, dont waste time if you want to upgrade the HV in your car do it with one of these and no other.

Check the link in my profile.

 

Bought a 100k mile '06 to fix up for my sister-in-law, who drives 50 miles each way to work and needed something more practical than her Cadillac SVT (an amazingly huge pile of dung). Car came cheap due to seller panicking over red triangle of death, along with amber ABS, VSC, etc. They took the car to their local dealer who pulled the usual, telling them they needed a new hybrid battery AND a new ABS pump, which they would happily replace for the bargain price of only $8,400. I took one of my rebuilt hybrid batteries and a good 12 volt with us to pick the car up. Ran Doctor Prius and my bi-directional scanner and got the expected codes before switching out the two batteries and scanning again. Cleared DTS and drove it home with no issues. Existing hybrid battery showed two failing modules, and as is often the case (in my experience) once the battery issues were resolved the other codes disappeared. I only mention the history because of the dealer's part, not that anyone here needs further warning.

So, sis-in-law has no patience with car problems, she just wants something reliable, and since her hubby died a few years ago, she's somehow become my responsibility (she's nice enough, I just like to bitch). After cleaning everything up, changing fluids, plugs, filters, etc. the car was looking and running great (48.5 mpg w/o trying), but I wanted my back-up battery back, so I decided to try a Nexcell upgrade. That was a year ago.

Since then she's put another 25k miles on the car without issue. She's all about her comfort, so pretty much A/C or heat running most every day, along with an upgraded stereo, phone charger, radar detector, and a tablet charging. Purely anecdotal, since I only check it every couple of weeks or so ('because she can't be trusted to check her oil level) but she's been averaging over 50 mpg while driving mostly 60-65 mph.

Ultimately sold the GM pile of crap for what I had in the refurbished Prius and the new battery modules (plus I got 26 serviceable modules for use on other batteries) . The car came to us with new Michelins, recent brakes and new wiper blades, so nothing else has been required other than a tag light, oil and filter changes. I now care for a dozen friends and family member's Prius models (Gen 2 & 3) so anything that makes my life easier is a win, and thus far, the Nexcell modules have been great.

That said, why would I need a V2 upgrade?

 

My cousin-in-law’s husband passed away, (also an in-law). Soon after it appears she had a new guy in her life. My wife’s family was pissed, and I had to remind her the vow is “until death do us part”. You’re a good person for taking care of her….

 

Azausa says the “battery is lighter and has more amps constantly” so you better upgrade!!!

 

They’re sold out, sigh.

Reasons for upgrading, quoting the text:

- A newly designed top cover that provides extra heat dissipation.

- A brand new circuit board that ensures the lithium remains at an optimal voltage level.

 

I forget where I saw it, but they are sold out for June as well.

 

Yeah, I received the notification and tried to order a few days later, but poof, all gone. Gonna try it out when I order my next battery (also sold out at the moment), which I understand will also be the v. 2.
I was just curious why I'd need an upgrade for something that has been operating flawlessly for about a year now, but, we live in a very moderate area where we thankfully don't see the weather extremes many others deal with, so there is that...

SM-N960U ?

 

Jerry, I have the original battery installed, with upgrade V2 ready to Install.
Do I have to deinstall the original battery completely in Order to upgrade to V2?

 

I think you quoted the wrong person?