Replacing 12V Battery with LiFePO4 (Video)

[knightmb]

Price aside, this BMS requirement is the reason I have not swapped. And even if the 12v has its own reliable BMS, I'm left with the problem of cold spells in the winter when the 12v cannot charge.

@stanton, how did your LFP handle the cold week in Texas ?

That is a good point, if you live in an area that will ever get far into the negatives for temperature then the lead acid/AGM is probably the only battery that can live below those temperatures without damage. The one I swapped into my Leaf has a limit of -31F (-35C), so luckily it never gets to those extremes where I live, so I've had good luck with my lithium 12v swap.

 

[SageBrush]

That is a good point, if you live in an area that will ever get far into the negatives for temperature then the lead acid/AGM is probably the only battery that can live below those temperatures without damage. The one I swapped into my Leaf has a limit of -31F (-35C), so luckily it never gets to those extremes where I live, so I've had good luck with my lithium 12v swap.

-31F is the operating limit; 25F (-4C) is the lowest temp the LFP will charge.

I imagine the problem is made worse by the otherwise most excellent flat voltage curve during discharge. When the LFP drops into the 'charge now' voltage range the SoC is really low. If that happens early in the evening and another 12 - 16 hours have to pass until the 12v case heats up from ambient, it is a window for battery damage.

No doubt about it -- LFP has a lot to offer. But I'm awful leery about an Ad-hoc replacement in a 4 season climate that the EV presumes is PbA.

 

[bobkart]

This is the battery I went with:
https://www.ohmmu.com/product-page/12v-lithium-battery-for-tesla-model-3

The link spec is 8.5 Lbs.
I was told by Ohmmu that they reduced the Ahr by half to ~ 20 Ahr so that their product would not cause alerts in the Tesla Model 3

I had a long discussion with them a few weeks ago that ended with them promising to perform a discharge test at 0.1C and to share the results with me. They did not keep their promise so I gave up on the idea of buying a battery from them for my Tesla

Looks like the specs drifted on the Model 3 version after they split off the Nissan Leaf version. The latter still has the 11-pound spec I saw. Odd that the Model 3 would have a problem with too much accessory battery capacity.

Sorry to hear that they dropped the ball on that discharge test. Actually I would have thought they would already have that data, but maybe not since lightening the battery. I still think they're good batteries (but on the expensive side), and the customer service I've experienced has been satisfactory. As far as I know, they work below freezing, but am not seeing a specific number in their specs. I know mine has been down to below 20F ambient a time or two, with no apparent ill effects. My impression is that they dope the chemistry somewhat to gain the lower-temperature-handling capabilities.

Regarding chemistries, LTO looks to have great service life and cycle count, and tolerates temperature extremes well (-40). Also has very high charge/discharge rates (~10C continuous). Somewhat less energy density than LiFePO4 though, with comparable safety regarding thermal runaway. At 2.3V nominal it takes five to make a 12V battery. With the right BMS I can see this being an even better automotive battery replacement option than LiFePO4. High cranking power (for ICE applications) should be easier to achieve than with LiFePO4.

 

[SageBrush]

As far as I know, they work below freezing, but am not seeing a specific number in their specs. I know mine has been down to below 20F ambient a time or two, with no apparent ill effects.

See my post above
https://mynissanleaf.com/viewtopic.php?f=37&t=29989&p=599863#p599853

 

[bobkart]

-31F is the operating limit; 25F (-4C) is the lowest temp the LFP will charge.

I see . . . are those numbers for 'generic' LFP, or specific to the Ohmmu batteries? Because my understanding is that it's possible to tweak the chemistry to improve various generic chemistry characteristics (often at the expense of other characteristics). Discharge rate is one of those. Low-temperature charging may be another.

 

[SageBrush]

-31F is the operating limit; 25F (-4C) is the lowest temp the LFP will charge.

I see . . . are those numbers for 'generic' LFP, or specific to the Ohmmu batteries? Because my understanding is that it's possible to tweak the chemistry to improve various generic chemistry characteristics (often at the expense of other characteristics). Discharge rate is one of those. Low-temperature charging may be another.

You can bet that Ohmmu buys generic cells and packages them.
Every time I read about LFP I come across the 25F charging restriction. While I doubt it is written in stone, for now it is pervasive.

I'm looking forward to learning how Tesla deals with the limit, now that they are putting LFP in the Model S and Model X. My 2¢ wager is that they added a way to heat the 12v case. The other possibility is that Tesla charges the 12v when the ambient is getting cold as a preventative step. That would work in my 'hood, but not in SK or Scandinavia.
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LIke you, I have no idea why a smaller Ahr capacity battery solved Ohmmu's Tesla Model 3 problems. I asked, but was given a BS answer.
FWIW though, Tesla monitors the 12v battery in the Model 3 and 'knows' when it is EOL. It does not seem to me to be a far stretch guess that the LFP was confusing the Tesla diagnostics. It is beyond me though to say how or why.

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I'm looking forward to seeing the 25F charge restriction solved, and for 12v LFP to drop in price with some competition and scale. For now the price approaches $1000 per kWh while cells are in the $100 per kWh range.

 

[LeftieBiker]

The other possibility is that Tesla charges the 12v when the ambient is getting cold as a preventative step.

This is what I would bet. Heating the battery tray would be the next step for frigid climates.

 

[SageBrush]

I just found this vendor
https://relionbattery.com/products/lithium/rb50-lt

They include a heating element in the case

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I'm not going to spend that amount of money for our LEAF, but if Tesla does not come through with an LFP for the Model 3, I'll be inclined to buy one for our Tesla. As an aside, some Googling suggests that LFP has low internal resistance. Does anyone know the LFP SoC when the car BMS throttles down, and subsequently disconnects the DC/DC converter ? This is one of the tricky parts because the car presumes PbA

 

[knightmb]

I just found this vendor
https://relionbattery.com/products/lithium/rb50-lt

They include a heating element in the case

--
I'm not going to spend that amount of money for our LEAF, but if Tesla does not come through with an LFP for the Model 3, I'll be inclined to buy one for our Tesla. As an aside, some Googling suggests that LFP has low internal resistance. Does anyone know the LFP SoC when the car BMS throttles down, and subsequently disconnects the DC/DC converter ? This is one of the tricky parts because the car presumes PbA

Interesting, so you can buy some off-the-shelf LFP with a built-in heater. Yeah, the capacity is overkill though, would probably need that to start a large engine, but if they made a smaller 20ah version for half or less the price that gets it closer to what I paid a decade ago for mine (without heater), though now the same battery/capacity I got is much cheaper now than what I paid. Isn't the original lead-acid that is used in the Leaf only rated at 30ah though? I'll have to check mine to see, but the actual power you get from the lead-acid is quite lower than the rating unfortunately, kinda like that for any lead-acid battery.

 

[SageBrush]

I just found this vendor
https://relionbattery.com/products/lithium/rb50-lt

They include a heating element in the case

--
I'm not going to spend that amount of money for our LEAF, but if Tesla does not come through with an LFP for the Model 3, I'll be inclined to buy one for our Tesla. As an aside, some Googling suggests that LFP has low internal resistance. Does anyone know the LFP SoC when the car BMS throttles down, and subsequently disconnects the DC/DC converter ? This is one of the tricky parts because the car presumes PbA

Interesting, so you can buy some off-the-shelf LFP with a built-in heater. Yeah, the capacity is overkill though, would probably need that to start a large engine, but if they made a smaller 20ah version for half or less the price that gets it closer to what I paid a decade ago for mine (without heater), though now the same battery/capacity I got is much cheaper now than what I paid. Isn't the original lead-acid that is used in the Leaf only rated at 30ah though? I'll have to check mine to see, but the actual power you get from the lead-acid is quite lower than the rating unfortunately, kinda like that for any lead-acid battery.

They sell smaller capacity batteries, for less money. Whether that is cheap enough for you is a ymmv.

I want a large capacity 12v for my Tesla because I think it would reduce "vampire" drain. That said, I may be barking up the wrong tree and instead should perhaps be looking for a battery with very low internal resistance. The best (I think) would be a battery that is *both* high capacity and low internal resistance, in a car that knows it is dealing with an LFP. Not there yet for the Tesla.

I agree that a 20 Ahr LFP battery that can handle the cold would probably work great in the LEAF and outlive the car. My LEAF is a 2013. It currently has a ****** walmart battery that is 3 years old that I am testing this week. I expect to either replace it soon or before the next winter. I figure that a better AGM PbA will last ~ 4 years, which is about how long I expect to keep our LEAF so the extra cost of an LFP has unclear benefit in my case. I've about decided on this replacement:
https://www.remybattery.com/batteries/brand/deka-intimidator/intimidator-car-and-truck-batteries/intimidator-9a51r-group-size-51r-agm-battery-html.html

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As an aside, LFP is cheaper than PbA on a kWh basis as a commodity. I don't know of any reason why LFP will not eventually be the cheapest and best option.

 

[knightmb]

I agree that a 20 Ahr LFP battery that can handle the cold would probably work great in the LEAF and outlive the car. My LEAF is a 2013. It currently has a ****** walmart battery that is 3 years old that I am testing this week. I expect to either replace it soon or before the next winter. I figure that a better AGM PbA will last ~ 4 years, which is about how long I expect to keep our LEAF so the extra cost of an LFP has unclear benefit in my case.

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As an aside, LFP is cheaper than PbA on a kWh basis as a commodity. I don't know of any reason why LFP will not eventually be the cheapest and best option.

Good advice. When I traded in my 2013 Leaf for a 2020 (in 2021), I just transferred my old LFP from the 2013 to the 2020 and put the new lead-acid the 2020 came with in storage with a tender. I did a capacity test on my old LFP (with was only rated for 20ah) before doing it because I wanted to see what nearly a decade of use had done to it capacity wise. To my surprise, it came up close to the original 20ah (technically I got 19.29 before it hit the safe discharge voltage cut-off) It cost a lot more years ago, but appears to be a good gamble with years of service without a single hiccup. Well worth it to me not to have to keep changing out lead-acid batteries over the years both labor and cost wise. :mrgreen:

 

[SageBrush]

I just transferred my old LFP from the 2013 to the 2020 and put the new lead-acid the 2020 came with in storage with a tender. I did a capacity test on my old LFP (with was only rated for 20ah) before doing it because I wanted to see what nearly a decade of use had done to it capacity wise. To my surprise, it came up close to the original 20ah (technically I got 19.29 before it hit the safe discharge voltage cut-off) It cost a lot more years ago, but appears to be a good gamble with years of service without a single hiccup. Well worth it to me not to have to keep changing out lead-acid batteries over the years both labor and cost wise. :mrgreen:

Yes indeed, and impressive report on longevity. The price is a lot more palatable when you have a reasonable expectation of being able to move an LFP 12v from current car to next car.

 

[Nubo]

... I figure that a better AGM PbA will last ~ 4 years, which is about how long I expect to keep our LEAF so the extra cost of an LFP has unclear benefit in my case. I've about decided on this replacement:
https://www.remybattery.com/batteries/brand/deka-intimidator/intimidator-car-and-truck-batteries/intimidator-9a51r-group-size-51r-agm-battery-html.html ...

92AH in a 51R Pb automotive battery? I suspect that's a mistake. Manufacturer's spec is 46AH (still good!)
https://www.eastpennmanufacturing.com/wp-content/uploads/0007-DEKA-SLI-Spec-Sheet.pdf

 

[SageBrush]

92AH in a 51R Pb automotive battery? I suspect that's a mistake.

Yeah, I saw that too.

They call it a 'rate' which I don't understand. Mostly I decided to ignore that number but my *guess* is that it is peak Amps for longer than the cranking Amps, extrapolated out to (the unachievable) one hour. Or something close but not interesting.

It reminded me of the Tesla advert of 1000 miles range per hour charging ... if you could manage 250 kW continuous for an hour, which you cannot.

 

[DentedLeafofUtica]

Thanks for the tip bobkart! I just replaced my almost completely dead 12v lead acid with an Ohmmu Leaf battery that was on sale. It's been an expensive year for her. She's a 2012 SL, made in 2011 in Japan, picked her up highly used in 2017. Hasn't needed anything until 2021, and then she needed everything over the course of the year: tires, tpms modules, pads, rotors, calipers, #1 water pump, parking brake actuator and now the 12v battery. If it happened all at once, I might have retired the vehicle. But now that I've had all of that done, I'm going to try to keep her running as is for as long as I can. Maybe in 3 or 4 years I can get a reasonably priced 40 or 60 kWH salvage battery to extend the life and range of the vehicle. Still like the car, as poorly designed as it is, but it's just an around town errand car with it's 20 to 30 mile, below zero degrees fahrenheit range. 50 miles at low speeds in the summer. It's too bad winter temperatures last 6 months of the year in upstate NY!

 

[alozzy]

...Maybe in 3 or 4 years I can get a reasonably priced 40 or 60 kWH salvage battery to extend the life and range of the vehicle...

You might want to consider Andre's EV shop in Quebec, as you would get a favorable USD -> CAD exchange price discount:

https://ve.simonandre.ca/leaf-2/

 

[DentedLeafofUtica]

You might want to consider Andre's EV shop in Quebec, as you would get a favorable USD -> CAD exchange price discount:

https://ve.simonandre.ca/leaf-2/

Thanks for the tip!

 

[k9spud]

I parked my Leaf for 4 days and returned to a dead 12V lead acid battery (and it was only 2 years old). Started reading about everybody having such a good time with LiFePO4 batteries and decided to get one.

I bought an "ECO-WORTHY 12V 30Ah 360 Wh 7.2 lbs LiFePO4" battery on sale at eBay for $125 after tax. That's cheaper than Wal-Mart's $150 lead acid battery, although higher than an Econocraft lead acid for $70 at AutoZone.

The sticker on my 30Ah LiFePO4 says max charge/discharge current 20A/25A, which sucks in my opinion (ACC mode with headlights and stuff turned on can easily exceed 30A). Sticker seems to claim the internal BMS will prevent charging below 0C, which is great if true. Freezing temperatures are rare but may happen once a year here in AZ.

I used a 23 ft length of 16 AWG copper wire to act as a current limiting resistor (about 0.09 ohms) so that when the car pushes 14.2V, it shouldn't exceed the 20A max charging current specification of my LiFePO4 battery. This works and I was still able to start the car with it, but voltage on the car side of the resistor sagged down to 11V briefly during start.

That seemed kind of crappy. I want the car's relays to snap strongly and not bounce, to prolong the life of the contactors. So I added a 15A diode in parallel to the resistor wire, so that the car can take current out of the battery without impedance. This was very satisfactory, no more big voltage sage during car starting. 15A is a little bit small, IMO, but it was the biggest diode I happened to have on hand. I'd recommend going bigger if possible.

My car is working nicely (as long as I don't use ACC mode with lots of stuff turned on), but I did notice the car constantly goes into 14.2V charging mode for 50 seconds (it used to just constantly float at 13.1V for the most part). Since LiFePO4's nominal voltage during the bulk of it's discharge curve is 12.8V, the car is constantly going 14.2V for 50 seconds, 13.1V for a few minutes, eventually sliding down to 12.8V, then repeating.

That seems dumb to me. Ideally, I'd like the car to let the battery voltage float down to 12.5V or more before initiating a recharge cycle. If I buy a really big LiFePO4 12V battery (with higher max charge/discharge current capability), the car should deep discharge the LiFePO4 battery during operation instead of using the high voltage traction battery to power the 12V rail. In my opinion, it should be possible to extend the range of the car a bit if we restrict the car to only recharge the 12V battery while connected to grid power.

Is it possible to take control of the Leaf's DC-DC converter with a CAN bus bridge? I'd be interested in getting one of those (if they ever become in-stock) and doing some firmware hacking to get this done.

 

[gibacca]

Been away from the forums forever, and the LiFePO4 batteries have caught my attention, as my 2019 SL Plus is now over 3 years old, and even though my OEM battery seems to be still good, the end may be near.

I'm looking for a self-heating battery in the 50Ah range that would fit in the 51R slot of the current battery. Amazingly, there are not that many good options out there (the best I found is some Chinese factory one that wants me to buy a bunch of them), and the ones that exist seem relatively expensive... Anybody know of a good self-heating replacement for the Leaf for let's say under $400? Would love to pick one up...

 

[LeftieBiker]

Why LiFePo4 as opposed to a good AGM for about half the cost, with no BMS to fail and kill the battery? Where (what region) do you live?