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I want to replace my cargo van's lead-acid battery with a LifePO4 battery. Never used any li-ion type battery for high amp burst.

The current lead-acid is NAPA The Legend Premium Battery BCI No. 75 690 A Wet, which is 850 Cranking Amp and 690 Cold Cranking Amp. I see some 50Ah LifePO4 battery has 100-amps 30-seconds continuous output. Theoretically, it is enough to replace that lead-acid.

The other thing that puzzles me is if I need to attach a battery charger for the lifepo4 or the car's alternator is appreciated as a charger.

Has anyone had experience with it? Which capacity should I go for?

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    \$\begingroup\$ Voting to close: "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." Having done that -- do a websearch. There are LiPo and probably LiFe batteries that are packaged into an automotive form factor, with appropriate circuitry so that they are drop-in replacements for lead-acid batteries. \$\endgroup\$
    – TimWescott
    Commented Nov 24, 2020 at 2:15
  • \$\begingroup\$ I believe that you will have problems trying to use a lifepo4 with a standard alternator. It will (or could) shorten the life of your battery. LiFePO4 is a great option for starter batteries, but only if the alternator can be controlled so it does not over-charge the battery and kill it. The engine compartment temp is also kind of warm. Not an expert so only commenting. \$\endgroup\$
    – user57037
    Commented Nov 24, 2020 at 2:22
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    \$\begingroup\$ There is also an automotive stack exchange. electronics.stackexchange.com/questions/137249/… \$\endgroup\$
    – user57037
    Commented Nov 24, 2020 at 2:23
  • \$\begingroup\$ I found some blogs that talk about either using a regulator to regulate the alternator or a more sophisticated BMS (expensive). I don't think there aren't many lifepo4 batteries with a built-in regulator. So I think it might not be cost-effective to do that. \$\endgroup\$ Commented Nov 24, 2020 at 6:30
  • \$\begingroup\$ @mkeith I didn't though about the tempature. You are right, it will kill the battery rather fast. \$\endgroup\$ Commented Nov 24, 2020 at 6:31

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Do not use LiFePo4 as a car battery, at or around freezing you will start doing permanent damage as the alternator tries to charge it. The solution is Lithium Titanate. you can purchase them from AliExpress (Alibaba is for businesses, they will sell it to you but use AliExpress first). Titanate can handle the extreme temperatures and has an insane charging/ discharging rate. the only problem is they are large cylindrical cells, you will need to relocate them through the firewall and maybe install it under a seat or build a box so someone doesn't kick it. for a 12v system usually 6 cells minimum are required, but since it's for a car you MIGHT need 1 extra cell because the alternator pumps out 14.4 volts I think. You will want to add balance wires to connect your battery bank to the BMS and you will want insanely large cables, I would try 4/0 first WITH a fuse and if it's not enough you will need THHN cable, it starts at 250 MCM and goes up really high. THNN is for buildings. for the proper fuse you will probably need a Class T fuse rated for the wire size. Consult a professional, you are playing with a battery chemistry more powerful than lifepo4 and larger capacity than most lithium ion except for vehicles. Almost forgot Titanate has an extreme cycle life, like 20,000, it will outlast your car. for comparison lifepo4 has an insane life cycle compared to Pb lead at 2,000 to 4,000 cycles. that translates to about 10+ years so do the math for titanate you can see what I mean

-an addendum: for lifepo4 you do not want to keep the cells at 100% SOC state of charge for a long time. it is harmful long term, and while it can survive going down to 0% SOC it is also not advised. it is usually set in the BMS battery management system as 2.5v for the cut-off voltage and if you limit the max capacity to around 90% or less your cells will last much longer. so the lower limit is about 10% SOC or more. again that's for lifepo4, TITANATE probably has another set of rules to follow, firstly follow the manufacturer specifications, it will be listed on the aliexpresss product page. also do a cross reference match for specs of similar cells. I have seen one manufacturer list lifepo4 as being able to tolerate temperatures well below freezing, that is an outlier and wrong, lithium is in it's infancy, even many manufacturers do not know what they are doing and their recommendations change like the weather. use common sense, cross reference specifications and read what other people on forums do, many are knowledgeable! also I suppose this is a "fun fact" (I hate that meme) lithium titanate is used in car sound competitions because it can handle the abuse, they also fill the vehicle walls with concrete for the sub-woofers

2nd addendum: forgot to mention you will burn out your alternator unless you introduce a charge controller of some sort. what you must do is find a device to limit the amps coming from the alternator because lithium batteries will attempt to pull as much current as the alternator can supply until it burns out unless the battery is already nearly full which than the BMS will cut off the charge according to your upper voltage limit that you chose as per the SOC chart for titanate. remember titanate has completely different voltages so do not attempt to use the same lifepo4 voltages examples I gave

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  • \$\begingroup\$ As you are posting the same answer to two questions it would be helpful if you could add some material to tailor this to the question. It's relevant in both cases but arguably could just have been a cross reference in one case. I'll upvote both :-). \$\endgroup\$
    – Russell McMahon
    Commented Apr 22, 2021 at 12:36
  • \$\begingroup\$ yes I did however consider that someone may not look at both questions and I am the only person to offer a real world solution. I have been researching lifepo4 cells for a while now and I know with certainty that the people saying "lifepo4 is perfect as a car starting battery" have absolutely no clue what they are talking about. also lifepo4 is not designed to be at over 90% state of charge for long periods, in fact somewhere near 50% is the ideal inactive storage, but for an active car the BMS can be set to 70-80% capacity max charge, there is a voltage chart to lookup the state of charge. \$\endgroup\$
    – eksine
    Commented Apr 23, 2021 at 20:03
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LiFePO4 is not suitable as a start battery. A start battery typically spends most of its life fully charged and then is asked to produce a brief burst of current to start an engine. This is an ideal regime for a lead acid battery.

If LiFePO4 is left for any length of time in a fully charged state it will adversely effect the life of the battery, they are much happier in a half charged or cycling state. The purchase cost is higher than lead acid and they require a carefully designed battery protection and charging system.

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  • \$\begingroup\$ Roy, I actually was under the impression that LiFe batteries are perfectly stable with full charge when left on a shelf... Do you have any reference that shows otherwise? \$\endgroup\$
    – MadHatter
    Commented Nov 24, 2020 at 15:36
  • \$\begingroup\$ qualitysource.co.uk/blogs/news/… also from the CALB battery manual they ship at 30% SOC and recommend storage at the same, there are other sources out there I will leave it to you to find them. \$\endgroup\$
    – RoyC
    Commented Nov 24, 2020 at 20:29
  • \$\begingroup\$ I think some systems can use a charging shutoff like the Victron device or more advanced BMS to achieve stability. But again, one it might be too expensive for just a starter battery even I just want to experiment it, two the temperature of the engine compartment is too high for a Li-ion battery. I didn't actually think about the temperature initially. \$\endgroup\$ Commented Nov 25, 2020 at 3:47
  • \$\begingroup\$ @MadHatter All recommendations I have seen is to store lithium batteries at half charge. That said, I have a batch A123 that have never been touched for 10 years now, maybe longer, and they all still read 3.3V (or 3.6V) as of 6 months ago, I can't remember. \$\endgroup\$
    – DKNguyen
    Commented Mar 23, 2021 at 4:53
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Many of the comments mix different chemistry batteries so it’s hard to say what is what.

Many comment say LiFePo batteries cannot be charge at a low temp, or can’t be kept a full charge, etc etc etc, blah blah blah (I’m not going into the gory details). But don’t many complete batteries have BMS that protect against these edge conditions?

As far as the battery not likely being at full charge, there is a simple solution. If your alternator thinks 14.4v is full charge configure your battery so that 14.4v is 70% (or whatever) charge. Probably put an extra cell in series.

All you want to do is get one start out of the battery at decently cold weather. Once the engine is started, the alternator takes over and can warm the LiFePo battery to working temp, the BMS should protect the battery.

As far as the temperatures in the engine compartment being too high, that’s not a big problem either. An insulated battery box, possibly with a fan pushing cool outside air around the battery. No doubt it will require a lot of testing and tweaking, but it seems doable.

BTW The batteries I have available are 50AH Valence U1-RT12 to be specific

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