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Back when I was a kid, car batteries used to be huge heavy lumps of plastic filled with lead and acid. They used to weigh almost as much as a mobile phone (slight exaggeration there, sorry).

45 years later, car batteries still look the same and weigh the same.

So, in this modern age and emphasis on fuel economy, why do batteries still weigh 40 lb? Why have advances in technology not been able to make them lighter and more efficient?

Peter Mortensen
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    Well, all the technology from 45 years ago isn't obsolete as of now. – dim Nov 18 '16 at 10:00
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    @dim? 45? More like 120 years... but yeah. We still build bridges out of steel, our concrete has gotten better, but still is essentially concrete, we use Asphalt for roads, copper is still our favourite conductor, the most commonly found amplifier technology in everything that isn't basically low-frequency is a bipolar-transistor based class A/B amplifier, we still burn oil to keep our homes warm, and our refrigerators still aren't based on Peltier elements, but on compressing more or less dangerous fluids. – Marcus Müller Nov 18 '16 at 10:12
  • @dim :) I extended my comment to illustrate my agreement with you :) – Marcus Müller Nov 18 '16 at 10:15
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    Imagine someone drives their car into yours and fractures your lead-acid battery. What do you get? You get a bit of acid leaking out onto the floor. Now imagine that with a Li-Ion. What do you get? You get a huge fireball that engulfs you and your family. Which would you choose? Ok, maybe that's an exaggeration, but you get the idea ;) – Majenko Nov 18 '16 at 11:28
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    Because the rest of the car is still 2000lbs of iron. If we were making 200lb cars of graphite/kevlar/epoxy and titanium, then 40lbs of battery would become more significant. –  Nov 18 '16 at 11:30
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    Well.... [the price](http://www.mylithiumbattery.com/shop/12v-lithium-ion-starter-battery/powerstart-12v-starter-battery-450cca/), oh, [the price](http://www.lithiumion-batteries.com/products/product/12v-50ah-lithium-ion-battery.php), and... [the price](http://www.obpltd.com/index.php?route=product/product&product_id=998) – J... Nov 18 '16 at 12:48
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    The latest batteries are much lighter and cost less over a vehicle lifetime. But they do not use LA (lead acid) chemistry. A LiFePO4 (Lithium Ferro Phosphate) battery will do what is required at acceptable whole of life cost BUT at higher initial capital cost - which makes it unattractive to car manufacturers. Cycle life is very much greater than that of LA. A "spike through the heart" will not cause the issues a LiIon has. Charging control is "easy enough". Allowed depth of discharge, & max acceptable charge rates are higher, temperature range better, recharge efficiency better. – Russell McMahon Nov 18 '16 at 13:00
  • Similar, but on a different stack: http://mechanics.stackexchange.com/questions/25752/replace-car-batteries-with-capacitors – anonymous2 Nov 18 '16 at 13:11
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    Batteries are among those few stubborn things that don't follow The Moore's Law. – Nick Alexeev Nov 18 '16 at 14:46
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    Lead Acid battery's work, they are relatively stable and don't require a lot of charging circuitry. And that is all you need. – Voltage Spike Nov 18 '16 at 16:53
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    Note that even hybrid cars that have big battery packs still tend to use a lead acid battery as a starting battery, so that should tell you something about the suitability of lead acid for this role. Though they tend to use AGM batteries, which are slightly lighter -- when I replaced my old flooded lead acid battery with a new AGM battery, the AGM battery was about 10% lighter (36 lbs instead of 41 lbs) – Johnny Nov 18 '16 at 19:09
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    @Marcus yet our concrete deteriorates quickly, while ancient Greeks had concrete that is still standing. – Passerby Nov 19 '16 at 02:21
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    @Passerby that is a gross oversimplification and pretty much, simply not true. I'm not a structural engineer, so I'm not going to praise concrete too much, but that's one of these ever over-used "the ancient did it better than us" cliches. – Marcus Müller Nov 19 '16 at 13:10
  • @Passerby (I might be a bit passionate about things like these, so please bear with my ranting :) ) Point is that what we call Roman Concrete (RC) (which I think you're referring to) is different from the types of Portland Concrete (PC) we use nowadays in chemistry. RC is less likely to form long cracks. However, it's pressure resistance, and thus, it's quality as material to build large structures seems to be inferior ("seems" b/c there's not 1 mixture,but a variety). Furthermore,PC is generally great b/c it has nearly the same thermal expansion as steel armaments–which is necessary. – Marcus Müller Nov 19 '16 at 13:31
  • Another [similar question from mechanics](http://mechanics.stackexchange.com/questions/19833/portable-jumpstart-kits-why-arent-regular-car-batteries-this-small) – barbecue Nov 19 '16 at 21:10
  • Definitely related: [Why is there so much fear surrounding LiPo batteries?](https://electronics.stackexchange.com/q/230155/5830) – user Nov 19 '16 at 21:27
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    A sort of meta answer to this (one that will give you a handle on how to think about these kinds of questions in general) is that non-trivial technologies have *long* requirements lists, and observing that a possible replacement system is better on *one* of them doesn't tell you much. You need to dig in and find the several limitation that characterize technologies and the breadth of the conditions under which the tech is expected to perform before you start a cost-benefit analysis. – dmckee --- ex-moderator kitten Nov 19 '16 at 22:06
  • https://techcrunch.com/2015/08/12/ohm-is-a-smarter-lighter-car-battery-that-works-with-your-existing-car/ – jamesdlin Nov 19 '16 at 22:52
  • An important point is that a lead-acid battery is much more robust and easier to maintain and manage with a relatively simple charge/discharge system. Only rudimentary voltage and current limiting is required when charging, and no exotic mechanism is required to limit the rate or "depth" of discharge. All other battery technologies are far more fragile. – Hot Licks Nov 21 '16 at 03:33
  • @Passerby That's no secret. Greeks only used concrete in compression, just like stone. We use reinforced concrete, which also undergoes tension and torsion - and the iron rusts over time. And don't forget that most of the Greek concrete buildings are either completely gone, or significantly damaged. A few buildings survived in decent condition, the rest is gone - that's just selection bias at its finest. And it's not like we have modern degraded concrete buildings - we replace them long before that. Compare the concrete fortifications from WWII - they don't have a scratch. – Luaan Nov 22 '16 at 09:24
  • The best battery for the money, IMO, is the Auto Zone Platinum battery. It is maintenance free and no acid to worry about. – Tim Spriggs Nov 22 '16 at 17:53
  • Why, just why is this being close-voted? What's the point in having knowledge and being an expert if you cannot reasonably answer questions like this? – sharptooth Nov 23 '16 at 10:47
  • @sharptooth - I really have no idea either. The vast majority of people who have been involved with this discussion seem to have somehow not got confused or found the question too broad.... –  Nov 23 '16 at 11:04

8 Answers8

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So, obvious answer first:

why do batteries still weigh 20kg?

Because they're still the same lead-acid batteries. Simple as that. No other technology came near the low cost per Ampere (and ampere-hour) of those, near the reliability and near the ease of handling. 20kg isn't that heavy, if you consider that "fuel economy" still means your average new car carries around dozens of kilogram of "comfort" functionality, and weighs around 1 Mg for the metal parts alone.

45 years later, car batteries still look the same and weigh the same.

45? More like 120 years... but yeah. We still build bridges out of steel, our concrete has gotten better, but still is essentially concrete, we use Asphalt for roads, copper is still our favourite conductor, the most commonly found amplifier technology in everything that isn't basically low-frequency is a bipolar-transistor based class A/B amplifier, and our refrigerators still aren't based on more efficient means of heat transport, but on compressing more or less dangerous fluids.

Marcus Müller
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    You're right, but the snark is a little unnecessary. – pjc50 Nov 18 '16 at 09:55
  • @pjc50 you're right. Reduced the snark. Moved the snark to my [second answer](http://electronics.stackexchange.com/a/270085/64158) – Marcus Müller Nov 18 '16 at 10:00
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    You should think a little more about the meaning of "why". It is unavoidably subjective, depending on the asker's starting viewpoint/premises. Why is the book in this position? Because John placed it there. Because it hasn't been put back on the shelf. Because I'm lazy. Because the table is 1.2m high, else it would have been at a different height (and therefore position). So many different "correct" answers. To truly answer a why question, you first have to know why* it was asked, and for that you have to somehow detect and understand the asker's perspective. (* yes yes..) – Museful Nov 18 '16 at 14:00
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    This answer gets a +1 from me due to Mg reference. – AndrejaKo Nov 18 '16 at 14:01
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    @Museful funny, that's why I wrote the other answer that answers the "why" that OP didn't really ask :) – Marcus Müller Nov 18 '16 at 15:06
  • I wonder if lead-acid batteries are really cheaper then other technologies if you take the lifetime cost into account? A car battery lasts 5 - 7 years, so might need to be replaced 3 times over the lifetime of a car. So a $150 battery actually costs $450 over the lifetime of the car. Is there another technology that costs $450 for a battery that lasts 15 years? – Johnny Nov 18 '16 at 19:14
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    @Johnny I assure you, I've never replaced a car battery after 1-2 years, and I've never spent $150 on one, and I don't think that's the production cost of a battery :) – Marcus Müller Nov 18 '16 at 19:40
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    Compressing fluids for a fridge - OR your car's AC - is still several times more efficient than Peltier refrigeration. –  Nov 18 '16 at 20:55
  • @BrianDrummond exactly! by means of power consumption, classical pressure-difference heat pumps are more efficient than the Peltier effect in practice. And in practice, with respect to cost, car batteries are more efficient than e.g. LiIon. I agree, I should've used a more efficient technology that's still not in widespread usage nowadays, to keep the series consistent. – Marcus Müller Nov 18 '16 at 21:00
  • "No other technology came near the low cost per Ampere" There's a technology called capacitors that do much better in cost per ampere than about any battery. – v7d8dpo4 Nov 19 '16 at 11:41
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    @v7d8dpo4 Please provide some examples for your claim! Supercapacitors with large short-circuit currents (say 100 A) suffer from large volume, high cost and low energy density. – AndrejaKo Nov 19 '16 at 12:07
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    @v7d8dpo4 that is simply, and plainly wrong. Of course, a cheap capacitor has a high current rating. But if you want to build a capacitor bank large enough to store energy to start your car, you will have an expensive day. Batteries are **far** cheaper per energy than supercaps! – Marcus Müller Nov 19 '16 at 13:15
  • _"we still burn oil to keep our homes warm"_ Well, no.. – Lightness Races in Orbit Nov 19 '16 at 18:53
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    @LightnessRacesinOrbit well, not *everyone* burns oil, indeed. But it's still a very convenient, save, reliable and cheap way of heating, and thus, very common. (maybe not where you are from – outer space – (or where your SO avatar is from – Krypton)) – Marcus Müller Nov 19 '16 at 18:58
  • @MarcusMüller: In the UK, oil heating is considered archaic. Gas is common, followed by inefficient electric heaters. I can't remember what we used on Krypton; it may have been krypton. – Lightness Races in Orbit Nov 19 '16 at 19:19
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    @LightnessRacesinOrbit Germany here; Oil is relatively common. see slide 9 of this [federal agency for energy report](https://www.bdew.de/internet.nsf/res/Pr%C3%A4sentation%20Heizungsmarkt-Studie/$file/Pr%C3%A4sentation%20Heizungsmarkt-Studie%20mit%20Sprechtexten_01072015_FINAL.pptx); says about 25% Oil, 50% gas of the households. <8% electric heatings. – Marcus Müller Nov 19 '16 at 19:24
  • @MarcusMüller: Meh, to me those numbers say "oil is relatively uncommon" ;) – Lightness Races in Orbit Nov 19 '16 at 19:34
  • For the record, see page 47 graph 6b [here](https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/345141/uk_housing_fact_file_2013.pdf) to see just how little Oil we use to heat our homes compared to other forms like Gas. – Lightness Races in Orbit Nov 19 '16 at 19:43
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    @LightnessRacesinOrbit "relatively uncommon" does not equal "no". Kerosene heaters are quite popular here. I use mine every year. – barbecue Nov 20 '16 at 00:50
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    I also question just how significant the distinction is between one fossil fuel and another. Coal, gas, or oil, all come out of the ground, and none of them are new or innovative. – barbecue Nov 20 '16 at 00:53
  • @barbecue: When we say "what we use" to do a thing, and "we" is the entire human race, and the answer is something still used by only a handful of people and on a massive decline versus a newer technology that is used by a substantial majority of that human race .... well, let's just say I think we interpret the original statement under discussion quite differently, and leave it at that. :) I would agree it's probably easier to just drop that particular example from the answer. – Lightness Races in Orbit Nov 20 '16 at 12:50
  • @LightnessRacesinOrbit good point. will drop. – Marcus Müller Nov 20 '16 at 12:53
  • @AnderaKo I only meant that capacitors (such as ceramic capacitors, not supercapacitors) do better than batteries in the max current they can handle. Not that they're better for powering a car. – v7d8dpo4 Nov 21 '16 at 06:24
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So, now after the answer to your literal question to your real question, that you sadly didn't ask

Battery technology has moved so far in the last 100 years. The lead-acid starter battery became common in cars in 1920, lead is essentially poison, and sulphuric/lead acid isn't any less dangerous. They tend to fail in cold temperatures, especially if not regularly maintained, and even though they're obviously cheap as hell to produce, the whole handling of them, including legal requirements to take back old batteries, must be a nightmare.

Why hasn't the industry just drawn a line and switched to things like LiIon or good ol' NiCd or NiMH batteries, now that electric cars have shown you can reliably drive years based on those?

The NiCd batteries are simply worse in every aspect but energy density than lead acid. NiMH is better, but much more expensive, and still has a higher rate of discharge, typically (unless you make them even more expensive). And still pretty hard to properly dispose of.

Lithium batteries aren't that easy handle. You need to protect them against all sorts of failures, and some of them are pretty fatal: don't overheat your lithium Battery. It will explode. And heat is a serious problem inside a motor compartment (in fairness, a battery doesn't have to be in there, but it's pretty handy).

The main reason really is cost. The battery in my last car, a 1999 Fiat Punto, supplied max 100 A (when I tried to estimate the actual short circuit current, around 43 A, but still a lot. Let's say P=U·I=12V·40A=480W) current, and had a nominal capacity of around 30 Ah (that's an energy of 12V·30Ah = 360Wh). It cost me 25€. So, rough guess, it's cheaper than 10€ to produce.

So, let's take a lithium battery type that is mass-produced and hence cheap. The commonly found round cells that make up many laptop battery packs are around 3€ each (let's say 1€ in production) for around 3Ah (11.1Wh), supplying up to 5A (tops, don't do that for long) at some 3.7 V. That says a single cell of these can supply 18.5W. So to reach the estimated 480W of my cheapo car battery, you'd need 26 of them. They'd cost 26€ in production, not counting the Euros you spend on control, charge and protection circuitry, on encasing them in something rigid and safe, and the fact that the minerals needed to produce some of the rare-metal components in Lithium batteries aren't currently getting cheaper, and equipping cars all over the world with those will definitely speed up that market mechanism.

Let's assume cost scales with capacity. My 26-cell lithium battery has 26·11.1Wh=288.6Wh energy. So we need to scale that by 1.25 to achieve the same 360Wh as the lead-acid battery.

Such a cell weighs around 90g. So the weight of the cells is 26·90 g = 2.34 kg. Ok, I don't have the exact weight of my cheap car battery in my head, but let's say it was 15 kg. So we saved weight by a factor of about 6.3, if our casing, and electronics are lightweight (they're not – as far as I can tell, you'll need a hefty switch mode power supply to be able to efficiently charge these using your car's generator, and those mainly consist of a pretty bulky coil of copper, and maybe some ferrite core that isn't exactly lightweight, either).

That leads to a cost factor of about 3.5 between component A and component alternative B, with handling disadvantages, lesser reliability and supply chain changes. No wonder the car industry isn't pushing in that direction. (And, by the way, they have excellent lobbying.)

Marcus Müller
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    I think 100A is uncommonly low for a car battery. Even 200A is small for a subcompact small car. Compacts and medium cars will easily be outfitted with batteries that can push 400-500A and higher, especially in cold weather climates where they need to still produce sufficient cranking amps at -30C or -40C. The high-current burst application is also very hard on lithium cells (unlike lead, which is extremely tough under this type of load). The list goes on... – J... Nov 18 '16 at 12:35
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    I think the WH of a starter battery isn't all that important.. nor the continuous discharge rate - rather the burst or 10s discharge (just enough to start your motor) would rather be the best measurement - I also agree with J in that 100A seems low, especially to start off with - still having100A after ~10 years is a lot more reasonable – user2813274 Nov 18 '16 at 12:56
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    I wot that a LiFePO4 battery will do what is required at acceptable whole of life cost BUT at higher initial capital cost - which makes it unattractive to car manufacturers. Cycle life is >> that of LA. Spike through the heart will not cause the issues a LiIon has. Max acceptable charge rates are higher, temperature range better, recharge efficiency better. – Russell McMahon Nov 18 '16 at 12:57
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    @J... note that I wasn't judging my battery by it's label. I connected a 1 Ohm heavy duty load resistor alone, measured current, then added a 0.7V voltage drop heavy-duty rectifier diode in series to that resistor. That gave me my source impedance and thus short circuit current estimate. And that definitely wasn't 100A. – Marcus Müller Nov 18 '16 at 15:09
  • @RussellMcMahon thanks for bringing LiFePO4 up - point is that I have zero experience with those, so I didn't write anything about them. – Marcus Müller Nov 18 '16 at 15:15
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    @MarcusMüller Surely, but likely your battery was old and rather heavily sulfated - certainly near EOL with performance like that. The point was that this is getting close to an absolute minimum of performance required in a replacement battery. The real demands of the application, with tolerance, aging, temperature, and safety factors, are undoubtably much higher. This is only to say that your estimate should be considered to fall on the cheapest and easiest side of the true requirement. – J... Nov 18 '16 at 15:31
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    @J... no questinos about that! bought it for 25€ four years before that. It barely worked, but it worked (lest things got too cold or I left the car standing for too long). So, I really picked the "worst lead acid battery that money could've bought four years before comparison". – Marcus Müller Nov 18 '16 at 15:34
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    _"don't overheat your lithium Battery. It will explode."_ - Also don't puncture it. It would be bad if a highway collision, which might normally cause severe-but-not-life-threatening injuries, caused both cars to violently explode... – BlueRaja - Danny Pflughoeft Nov 18 '16 at 16:27
  • @BlueRaja-DannyPflughoeft indeed, but to be fair, the problem does seem manageable by throwing money at it – there's not that many electric cars 'sploding these days. – Marcus Müller Nov 18 '16 at 16:29
  • Also, when you crash your car, lead acid batteries do not explode. – SnakeDoc Nov 18 '16 at 23:33
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    It seems to me that while we still use lead-acid batteries for all the reasons listed on this page, those batteries have gotten a little smaller (and thus lighter). – Adrian McCarthy Nov 19 '16 at 00:46
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    @AdrianMcCarthy indeed, they did. There's also stabilizing agents, knowledge on how to minimze whiskers and improved fabrication techniques that allowed to reduce lead that doesn't actually participate in the chemical reactions or current transport. – Marcus Müller Nov 19 '16 at 01:34
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    @MarcusMüller Was that 1 ohm resistor test done on a car battery? Considering I=U/R=12/1=12 A, 1 ohm seems very much too low as an approximation of a short-circuit condition in this case. – nitro2k01 Nov 22 '16 at 01:47
  • Would it be practical to use a supercapacitor to start the car and then a smaller Li-Ion or LiPo battery to power everything else? – Caleb Reister Nov 26 '16 at 08:17
  • @CalebReister Practical: yes. by any means cost-efficient: no. Easier to handle, more reliable or significantly smaller than your lead-acid battery: probably not. – Marcus Müller Nov 26 '16 at 08:43
  • I know this is an old answer, but 18650s can be tuned to provide high mAh or high impulse amperage. It's easy enough to find a single 18650 rated for 25A continuous discharge (and pulse numbers up to 100A for 5-6 sec), not 5A. The capacity figures will be 2800mah or so, instead of the 3300mah you'll find for laptop batteries. – Bryan Boettcher Feb 06 '17 at 22:19
  • @insta sorry, but you can do that for a couple of times with a 18650 (these are exactly the cells I referred to), but basically shorting them does damage them, and you'll drastically reduce the lifetime of your LiIon battery if you use them in overcurrent settings. That's why I mentioned those. – Marcus Müller Feb 06 '17 at 22:20
  • @MarcusMüller: that's not an overcurrent though. These are the kinds of cells designed for power tool battery packs, and are legitimately rated by the name-brand manufacturers for 20-25A continuous discharge through the entire capacity of the cell. The pulsed currents are on a derating curve, which is governed by heat. – Bryan Boettcher Feb 06 '17 at 22:23
  • @insta huh, I'm surprised! but yeah, trading capacity density for power density would result in such a cell, makes sense. – Marcus Müller Feb 06 '17 at 22:32
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    @MarcusMüller: they really are. Check out the Sony US18650VCT5A. It's 2500mah @ 25A continuously! A far cry from the aging Panasonic NCR18650B with its 3300mah @ 6A. Prices on eBay are comparable for the two cells, too. If you *really* need that extra 700-900mah per cell, you lose a LOT of continuous current. I think it's moreso that the INR chemistry is catching up to the NCR chemistry for capacity. – Bryan Boettcher Feb 06 '17 at 22:35
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The latest batteries are much lighter and cost less over a vehicle lifetime than ones of yore. But they do not use LA (lead acid) chemistry.

A LiFePO4 (Lithium Ferro Phosphate) battery will do what is required at acceptable whole of life cost BUT at higher initial capital cost - which makes it unattractive to car manufacturers.

Low initial capital cost seems to be the main reason to prefer lead-acid to LiFeO4 and it's not obvious that there are any other really good reasons.

Cycle life is very much greater than that of Lead Acid, which allows whole of life cost to be lower than lead acid.

Unlike LiIon (Lithium Ion) a "spike through the heart" will not cause the issues a LiIon has.

Charging control is "easy enough".

Compared to lead-acid:

Allowed depth of discharge, & max acceptable charge rates are higher,

Temperature range is better

Recharge efficiency is better.

Self discharge performance is better.

____________________________________________

Lithium Ion / LiIon:

It's worth commenting on LiIon batteries as they often get "bad press" with respect to safety.

Compared to lead-acid, LiIon chemistry offer substantially better mass and energy densities (lighter & smaller), somewhat longer cycle life, higher capital cost and probably somewhat superior whole of life cost. Properly managed, charging control is easier. Temperature ranges are better, charge/discharge efficiency is somewhat superior. Disdavantages relating to safety are largely not an issue - see below.

In many applications LiIon batteries are the battery of choice - from Dreamliners to Samsung phones to "Hoverboards", Mars Rovers to laptops and smartphones to MP3 players and more. The first three applications above were selected for their known spectacular failures. But anything used in a Mars Rover is chosen for its suitability in a long life, hostile environment, must not fail task. And there are hundreds of millions of LiIon batteries in everyday use in people's pockets and homes and cars and more.

Given the ways in which LiIon batteries CAN fail, the numbers that DO fail in a spectacular manner are very rare. Failures that are widely reported are quite often due to some systemic failure that affects a batch or model of battery that has been produced and distributed in vast quantities OR lower volume bu high profile applications. In such cases a design or manufacturing fault or shortcoming causes or allows failures whose consequences are exacerbated by the LiIon chemistry's unforgiving behaviors.

Examples are well publicised "vent with flame" events in some past Apple laptops, Samsung phones, self-balancing "hoverboards" and similar. In the 1st two examples usually competent manufacturers allowed a design fault to exist uncorrected and/or unnoticed or cut corners in manufacturing to the extent that safety margins caught up with them. In the case of the "hoverboards" the cause is unknown to me but is as liable to be low quality low cost manufacture and poor charge control as anything else. In consumer equipment LiIon battery failures often result from a short circuit occurring in a cell due to inadequate clearances and either consequent impact sensitivity or hitting the far end of statistical manufacturing tolerance variations. These are design and manufacturing errors that can be avoided at the cost of extra $ - something high volume manufacturers would love to avoid.

In the case of the Boeing Dreamliner battery failures I've not seen a final root-cause report BUT while a number of well publicised failures occurred (and maybe a few unpublicised ones) in a very small product volume, the consequences were astoundingly well contained.

A detailed examination of LiIon failures and modes and consequences shows that they are almost invariably nowhere near as violent as popular 'myth' suggests and that while the energy release is substantial, containment is relatively easy in engineering terms. Containment adds weight and volume and cost and is unlikley to be found in laptops or pocketable / portable devices. It IS found in Dreamliners and could easily be used in automotive single battery (ie non-EV) applications while keeping weight and volume still well below lead-acid levels and at modest extra cost. In electric vehicle applications the problems seem to have been solved or accommodated "well enough". I have ni expertise in vehiclar safety regulatory areas, but am confident that the regulations that bring us spectacular crash-dummy footage and allow the catting of high volatility petroleum fuels in passenger vehicles also address the safety issues around LiIon power sources. I have not heard of a 'Tesla' car being immolated through battery failure - although it may have happened - and I imagine that Musk and co believe they have this risk area "adequately in hand".

I have never, somewhat to my disappointment, seen a LiIon vent-with-flame event and do not personally know anyone who has. Occurrences are common enough to occasionally make the NZ news (NZ population is under 5 million).

LiIon versus LiFePO4:

Compared to LiFePO4, LiIon chemistry offers somewhat better mass and energy densities (somewhat lighter & smaller), substantially LOWER cycle life, slightly lower capital cost (per energy capacity), and substantially inferior whole of life cost. Charging control is about the same but LiFePO4 are significantly harder to damage in marginal cases. Temperature ranges are not as good, charge/discharge efficiency is about the same. LiFePO4 are far less subject to safety issues.

In areas where smallest size and weight and lowest capital cost matter (with electric vehicle use being a good example) LiIon are superior to LiFePO4.

In almost all other areas and applications, LiFePO4 are better or much better than LiIon and I'd consider them the current battery technology of choice for high energy long lifetime, high cycle count energy storage.

Russell McMahon
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    Basically, all of the above is true, but simply doesn't offer enough of a compelling reason to spend literally billions of dollars replacing the entire battery supply chain for the auto industry. LA batteries have survived because they do the job well, and all the infrastructure to use them is in place. Even in motorbikes, where weight is *far* more a consideration than cars (~0.2 vs ~2 tons gross vehicle weight) LA is still king. – Leliel Nov 21 '16 at 01:24
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    @Leliel A common enough means of introduction of new technologies is for early innovators to bypass the "supply chain" of the old tech and compete head on. Sometimes the attempt fails but often enough not. eg The 40V+ automotive supply proposals of a while back seem to have vanished without trace. Side-valve technology may be still found on Harleys (is it?) and lawn mowers and such but is otherwise long gone. | As above "I wot that a LiFePO4 battery will do what is required at acceptable whole of life cost BUT at higher initial capital cost - which makes it unattractive to car manufacturers." – Russell McMahon Nov 21 '16 at 08:16
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    It's not just the capital cost that's putting the auto manufacturers off. It's that the capital cost is *huge*, and benefits slim to none. LA is simply good enough, and already in place. Li doesn't offer enough benefit to justify the costs. – Leliel Nov 21 '16 at 18:19
  • @RussellMcMahon The 48V technology is implemented in the Audi SQ7. The SQ7 has a electrical compressor in addition to a turbocharger and needs so much energy that they needed more than 12V. But that is the only car I knew with 48V. – Sunzi Nov 21 '16 at 19:42
  • @Leliel, it appears you are saying the exact same thing as Russel. If all auto manufacturers switched to LiFePO4, it wouldn't be much more expensive LA. Like you (and Russel) said, the huge startup costs make it unfeasible. That said, if a great Tesla-like company came up with drop-in replacements that would literally last 3-5 times as long as LA and could afford to market it and sell at a slight loss, they could make it. – Joshua Nurczyk Nov 22 '16 at 11:23
  • @Leliel seeing you keep responding with claims but no real data (that I've noticed) it's probably useful (if never pleasing) to say that I basically disagree with your assertions. I may be wrong (although I do not believe so) but if you want to usefully exchange in tit-for-tat response you probably need to add some supporting data. I have offered comparisons rather than absolute $ above as the market keeps changing (Li based cells are continually dropping in kWh cost) but in absolute terms a retail 40 Ah 12V LA battery here probably costs $NZ150 retail. A 40 Ah LiFePO4 retail is perhaps $NZ400 – Russell McMahon Nov 23 '16 at 11:24
  • ... The LiFePO4 will last 2000 reasonably deep discharge cycles and probably the whole life of an average car in automotive use. (Say 10-20 years).The L' can be much deeper discharged without damage so equivalent capacity is higher so you can probably halve the capacity and capial cost for a fair comparison. You can but LiFeYPO4 batteries (note the added Y for Yittrium) now that claim direct drop in LA replacement. A regulator for LiFePO4 costs no more than for LA and possibly less. L' is better behaved in all the areas I listed in my answer an perhaps the ONLY "disadvantage" compared to ... – Russell McMahon Nov 23 '16 at 11:29
  • ... LA is capital cost. || If you can drop a LiFeYPO4 battery into a lead acid application, the whole of life cost is lower and all technical aspects are superior, how is LA in any way better except the per vehicle capital cost. ||| A look around ebay suggests that a LiFePO4 battery with BUILT IN BMS cost 2x to 3x LA AGM deep cycle of equivalent usable cycle capacity. Cost relative to car batteries would be greater as car battery is of lower spec and lifetime. Against that as well as lonnnnng life you get all the other benefits. Internal BMS balancing etc does no harm . – Russell McMahon Nov 23 '16 at 11:46
  • @RussellMcMahon According to http://www.oica.net/category/production-statistics/ total vehicle production is around 46 million vehicles per year. In order to convert all new production to Li chemistries, suitable battery production plants need to be built to meet this demand. Those don't exist yet. Tesla's new battery factory (https://en.wikipedia.org/wiki/Gigafactory_1) is estimated to cost on the order of $5 billion to build and equip to provide batteries for something less than 100K vehicles per year.. to be continued – Leliel Nov 23 '16 at 16:16
  • Contiued.. So we can see scaling out the production of suitable LI batteries to meet vehicle demand will cost on the order of billions of dollars to complete. All the improvements LI chemistries offer don't amount to much of a motivation to the car industry, as lead acid replacement costs aren't generally a major pain point for drivers. It's simply cheap enough to be a small part of the running costs for any vehicle. – Leliel Nov 23 '16 at 16:21
  • Missed the edit window. LA batteries last for 3 to 10 years generally, depending on how well they're treated (less if abused badly) and cost somewhere under $200 in most locations. My motorbike will eat $1200 worth of tyres in 3 years, so battery cost just isn't a big factor. over 10 years, it's more like $6000 in tyres. Plus all other maintenance and fuelling costs. Of course, you're completely correct about the technical advantages, they just don't add up to enough to justify the investment. – Leliel Nov 23 '16 at 16:28
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Lithium starter batteries exist, primarily for racing or other performance or luxury applications where the weight savings or bragging rights are worth the cost.

As others have noted, however, the demands of the application are rather extreme and lithium technology needs a lot of special development and care to be able to reliably and safely fulfil the role of a starter/accessory battery in a motor vehicle. The prices are extremely high - easily ten to twenty times the cost of a normal lead battery. Most people don't want to pay $1000 for their car battery, so they don't.

J...
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  • If the battery lasts 10x the time (so, 20-30 years), I would be _interested_. Though really only if I was buying a new car. – Wayne Werner Nov 21 '16 at 14:40
  • Taking in to account the number destroyed in accidents, the proportion of cars lasting 20~30 year is tiny. And a decent LA battery will last a lot longer that the 2~3 years your comment implies (battery in my car is the original one, and is over 9 years old) – Kickstart Nov 21 '16 at 17:17
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    @Kickstart That depends heavily on the economy of the country, but yeah, 30 years is still pushing it. And importantly, LA battery maintenance is quite trivial - when the communists ruled here, you didn't just throw out the battery - you wouldn't get replacement parts! Instead, you replaced the acid, cleaned the battery and it was as good as new. Try doing that with a lithium battery (disclaimer: don't - made of explodium). – Luaan Nov 22 '16 at 09:35
  • If you live in a really cold or really hot environment (neither of which are good for LA, and both of which I've lived in) only top of the line batteries last more than 3-5 years, and even then I've never had one last more than 6. – Joshua Nurczyk Nov 22 '16 at 11:31
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The answer is very simple: Because we haven't found anything better.

A car battery needs to hold its charge over a long period of time, be able to deliver a huge current and fit into a small space. And it would help if it's not too expensive.

Lead acid is still the best solution for those requirements.

You could use a Lithium based chemistry, they can hold the charge and deliver large currents. They are also far more expensive, temperature sensitive, require more care electrically, and are more spectacular if mishandled electrically or mechanically.
The extra costs and complexity are simply not worth the benefits of a < 1% reduction in the cars final mass.

Andrew
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    As you say, 1% mass reduction in car, not worth it. 1% mass reduction in airplane, worth it, if you can stop it catching fire as a consequence! – Neil_UK Nov 18 '16 at 09:50
  • As a clarification: Li-based batteries are less cold-sensitive than Lead-acid, but more heat sensitive. – Joshua Nurczyk Nov 22 '16 at 11:25
  • Li based batteries don't work at -40°, or even -30°. Automotive batteries are required to work at these temperatures - admittedly not many places need that. – Kevin White Feb 06 '17 at 23:00
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I saw that you added a new question to the end of your post:

Why have advances in technology not been able to make them lighter and more efficient?

Because that's not how chemistry works.

Capacity in a single type of battery is pretty much defined by the amount of ions that you have - and that is, in the case of lead-acid batteries, pretty much the mass of lead you need, plus some to keep the structure intact.

Now, other battery types suffer from a lack of surface or a limited ion mobility that limit those battery's ability to source a high current, but there's not much you can do to increase that for the lead acid battery – water is an excellent carrier for the chemicals involved, and the current sourcing ability of a lead acid battery is pretty much at its maximum.

Hence, it's simply a mature technology. Just like we haven't made cheap construction steel much better in the last 80 years, there's not much that can be done about lead-acid batteries to make them better without abandoning the lead-acid principle, with all the problems my second answer explains.

Marcus Müller
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Using supercapacitor as starter battery is fully feasible and was tried by enthusiasts in practice, see example. Aside from higher price, some examples of practical difficulties are reported:

  • Supercap alone, while starting the car more easily than lead battery, will discharge in about half a hour of listening to radio if not continuously charged.
  • Directly connected lithium battery+supercap combo does not suffer from above but ended up damaged when he used it to jumpstart a lawnmower - the Li battery would need extra electronics to prevent this.
Juraj
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Mainly one reason: price. There are technologically better alternatives, like lithium-ion batteries used in electric cars, but they are also much more expensive. These batteries are absolutely needed in electric cars where you need a huge capacity without increasing a lot the weight of the vehicle (lead batteries would be too heavy if they had to replace the fuel tank as the only energy supply for the car), but in fuel powered cars the weight of a single classical lead battery that is used just for starting the motor, compared to the car weight is not significant, while the price/capacity ratio is dramatically lower. It's a cost/efficiency issue: they're cheaper, they provide enough energy for the car needs, and its weight is not relevant. Weight and size only become relevant compared to price when you increase some thousands times the electric capacity needs.

user143522
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