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Anyone interested in 12V Lithium battery pack for their Model S?

ElectricLove

Member
May 28, 2013
554
314
Hi,

I work for a Critical Power Systems company and we are currently branching into the development of Lithium Ion battery solutions. We had a request from a Tesla Model S owner to start investigating the potential of a new custom built Lithium battery pack specifically designed for the Tesla Model S.

The request was for a 12V 40Ah capacity Lithium battery.

I'd love to know a few things:

1. Is there a large following for a product like this? (ie. are there many owners whom would be interested in purchasing such a battery pack, please speak for yourself rather than speak for others)
2. Are there any specific design criteria people would like to see? (ie. larger than 40Ah, less than 40Ah, built in 120VAC inverter or 12V cigarette outlet for the frunk, etc...)
3. What price point would people be interested in buying at?

Thank you very much, please email me at [email protected] if you'd like to discuss further directly with me, otherwise I really appreciate any/all feedback I may receive on this thread!
 

glhs272

Unnamed plug faced villian
Aug 21, 2013
909
564
Burlington, WI
Considering that my car is now out of warranty, when my battery needs replacing it will be on my own dime. At that point I would be interested in a battery that I won't have to replace again. Needs to be cold weather tolerant and compatible with the Model S's 12 volt charging behavior. Other than that, just a straight up drop-in replacement as far as features go. Less than $500 would be nice.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
It would be the 12V accessory battery, to replace the lead-acid version you currently get from Tesla. The Lithium version would be lighter, last longer and hold more energy.

You do know the current 12 volt lead acid battery is discharged about 50% and recharged to 100% 1/2 dozen times every single day, right? For a typical 500 discharge/charge cycle life that works out to about 160 days.
 

JRP3

Hyperactive Member
Aug 20, 2007
20,304
46,822
Central New York
I'd think LiFePO4 or Li titanate would be good choices since both should be good for thousands of cycles. Also the lithium battery would have an actual larger usable capacity, so each cycle would be a shallow cycle, further increasing cycle life.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,813
23,173
Texas
Once the car is out of warranty and out of maintenance, there will be considerable interest. As long as Tesla is replacing and not charging, not so much. I'm not particularly interested in more than just the battery. I'd suggest it would have to work with the current charging algorithm.
 

ElectricLove

Member
May 28, 2013
554
314
50-100% isn't a "full" cycle by the standards used to define cycle-life in Lithium batteries, it is pretty darn close to the cycle definition for lead acid though as they are not really rated for a deep discharge. One of the nice things about designing a custom pack is that we can make that 50%-100% a much larger "volume" and that will result in fewer partial cycles. We can also figure out exactly what the Tesla is considering 50% and 100% (based on voltage, the only thing the Tesla sees from the battery) and set those points to represent 40% and 80% on the new pack...

Any technical information like this that anyone has is great to share as it will improve our ability to meet the challenges of this specific system and develop a full-coverage solution!
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
50-100% isn't a "full" cycle by the standards used to define cycle-life in Lithium batteries, it is pretty darn close to the cycle definition for lead acid though as they are not really rated for a deep discharge. One of the nice things about designing a custom pack is that we can make that 50%-100% a much larger "volume" and that will result in fewer partial cycles. We can also figure out exactly what the Tesla is considering 50% and 100% (based on voltage, the only thing the Tesla sees from the battery) and set those points to represent 40% and 80% on the new pack...

Any technical information like this that anyone has is great to share as it will improve our ability to meet the challenges of this specific system and develop a full-coverage solution!

If 50-100% counted as a full cycle then we'd down to just over 80 days. Of course theres no hard and fast 500 charge rule, but that is often used as a rule of thumb in lieu of some electrolyte or anode additive that extends battery life. I was just mentioning it in case they weren't aware that the 12 volt accessory battery is continually charged and discharged.
 

ElectricLove

Member
May 28, 2013
554
314
I'd think LiFePO4 or Li titanate would be good choices since both should be good for thousands of cycles. Also the lithium battery would have an actual larger usable capacity, so each cycle would be a shallow cycle, further increasing cycle life.

LiFePO4 and Li-titanate are both fantastic battery choices, they are heavier though, which reduces our ability to say we are saving weight (though maybe that isn't really all that important).

We have looked into these battery technologies and compared/contrasted with the current offerings of INR-Hybrid chemistry 18650 cells (similar to what is used in the traction battery pack in the Tesla), the INR is more cost competitive because it is built in such volume (same reason Tesla is using in the main pack); The INR cells we have identified (LG HG2 or MJ1) are rated for around 500 FULL cycles at greater than 1C discharge (that means full to empty in 1 hour or less); in the Tesla Model S it will not be discharging at that high of a rate and it won't be discharging that deeply, this means the cycle-life prediction would be exponentially higher (it follows a curve rather than linear progression); LG hasn't tested in this application for life-cycle.
 

JRP3

Hyperactive Member
Aug 20, 2007
20,304
46,822
Central New York
LiFePO4 and Li-titanate are both fantastic battery choices, they are heavier though, which reduces our ability to say we are saving weight (though maybe that isn't really all that important).

My impression is that battery life is more important than the few pounds that could be saved.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,813
23,173
Texas
LiFePO4 and Li-titanate are both fantastic battery choices, they are heavier though, which reduces our ability to say we are saving weight (though maybe that isn't really all that important).

The Model S weights a bit less than 2250 kg (depending upon model). +-10 kg isn't going to be significant.
 

qwertzy

Member
Mar 11, 2015
125
23
Jamaica,NY
I can't wait for a 12v battery that can power all the accessories of the car, while fitting in the palm of your hand.

71c4a581-27bb-4877-8e12-2fe5cb90815d_400.jpg
 

ElectricLove

Member
May 28, 2013
554
314
I can't wait for a 12v battery that can power all the accessories of the car, while fitting in the palm of your hand.

View attachment 95966

Similar cells as we will be using!

- - - Updated - - -

My impression is that battery life is more important than the few pounds that could be saved.

I agree, one of the other things to consider is that the higher energy density battery will result in fewer cycles overall; this may work out to give a similar battery life as it stands. Beyond that when cells are rated for a # of cycles they aren't kaputs at the end, they have reduced capacity, they will keep cycling, the larger the initial capacity the larger the residual capacity and therefore the longer it will remain functional in its application... Those two things make me lean towards the larger capacity, when you fuse that with the lower price due to production volume, I feel you have a win-win... But we are open to whatever the community on the whole demands!

The goal is to provide a mission-specific battery for this application that will give people what they need and also keep the price (per kWh) low enough to make sense to buy from us. I know there are other manufacturers of standard 12V Lithium drop-in batteries, but they are designed with a more general approach and additionally tend to be a lot more expensive than we anticipate (for example Valence 12.8V 40Ah batteries are around $800)
 

ElectricLove

Member
May 28, 2013
554
314
I am interested in a Li replacement battery for the Lead Acid type in the car.
Weight saving is a priority in my Porsche at the track, but not for the Tesla Model S.
Perhaps something like this motorsport version: http://press.porsche.com/news/release.php?id=510

Doable! Those batteries are simple Li-Fe-PO4 batteries, I'll bet the pricing is in the thousands for one of those batteries though! I wonder if our batteries could ever look so sexy, my goodness!!!

One of the tricksy things that the industry does with these is rate them at a "lead acid equivalent"; ie they may say a battery is a 40Ah Lead Acid equivalent Lithium battery; all that means is that it can handle the same loads as a 40Ah Lead-Acid, but the actual capacity is much lower.

This Porsche battery is only about 18Ah capacity, the pack I'm working on for the Tesla will be a 40Ah capacity, more than double the capacity of that battery!
 

rickgt

Enthusiast owner/member
Dec 13, 2014
340
20
Carmel
I would be interested in this... I know others have had issues where the 12v battery fails and needs replacing. My car is too new for this yet, but by the time you have it available I should be in the market for it. Thanks
 

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