Reverse Engineering A Nissan Leaf Battery Pack

Batteries wear out. If you are an electric vehicle enthusiast, it’s a certainty that at some time in your not-too-distant future there will be a point at which your vehicle’s batteries have reached the end of their lives and will need to be replaced. If you have bought a new electric vehicle the chances are that you will be signed up to a leasing deal with the manufacturer which will take care of this replacement, but if you have an older vehicle this is likely to be an expensive moment.

Fortunately there is a tempting solution. As an increasing number of electric vehicles from large manufacturers appear on our roads, a corresponding number of them have become available on the scrap market from accident damage. It is thus not impossible to secure a fairly new lithium-ion battery pack from a modern electric car, and for a significantly lower price than you would pay for new cells. As always though, there is a snag. Such packs are designed only for the cars they came with, and have proprietary connectors and protocols with which they communicate with their host vehicle. Fitting them to another car is thus not a task for the faint hearted.

Hackaday reader [Wolf] has an electric truck, a Solectria E10. It has a set of elderly lead-acid batteries and would benefit hugely from an upgrade to lithium-ion. He secured a battery pack from a 2013 Nissan Leaf electric car, and he set about reverse engineering its battery management system (BMS). The Solectria will use a different battery configuration from the Leaf, so while he would like to use the Leaf’s BMS, he has had to reverse engineer its protocols so that he can replace its Nissan microcontroller with one of his own.

His description of the reverse engineering process is lengthy and detailed, and with its many photos and videos is well worth a read. He employs some clever techniques, such as making his own hardware simulation of a Li-ion cell so that he can supply the BMS known values that he can then sniff from the serial data stream.

We’ve covered quite a few EV batteries here at Hackaday. Quite recently we even covered another truck conversion using Leaf batteries, and last year we featured a Leaf battery teardown. We’ve not restricted ourselves to Nissan though, for example here’s a similar process with a Tesla Model S pack.

34 thoughts on “Reverse Engineering A Nissan Leaf Battery Pack

  1. This is going to be more common in the future, as (if) we get more electric cars, there will me more old battery packs that need to be replaced and there will be more people rebuilding/repurposing battery packs. I remember getting a battery for the car (starter battery, gas powered car) from a guy who rebuilt batteries as his business, it worked real good too, so it only makes sense people will start rebuilding electric car battery packs and selling them cheaper than the OEM packs.

    1. Sorry, but the article is just FUD. The battery packs in EVs typically outlast the car. For example, Tesla have tested their batteries up to 750,000 miles with 86% capacity remaining (Panasonic estimate 900,000 miles to 80%, which seems about right). Nissan have not released that much data but there are taxi firms with Leafs on 150,000 miles and less than 20% capacity loss.

      Also, replacement packs won’t be too expensive. They will be available used of course, and you can sell the “dead” pack for immediate use somewhere else like a home battery for storing solar energy or whole house UPS. 80% capacity remaining in a relatively small Leaf battery is still over 19kWh, way more than you need for home use.

      1. ….and your average car motor is supposed to last the life of the car too.

        But they don’t. Because Samsung and Tesla are testing their batteries in a ‘Perfect’ setting, and don’t account for unknowns and changing environment.

        They can say they will last that long all they want, I’m willing to bet that they won’t. Too many unknowns to account for, and too many distinct possibilities. And batteries do fail, often without warning and sometimes in very catastrophic ways.

        Oh, and you have to eliminate the dead cells if you want the pack to be worth anything. Take Laptop Li-Ion cells, most laptops have 6-8 cells in their battery. If a single cell fails, that’s it, the battery is worthless, and unless you are willing to tear down the battery and find the dead cell and replace/remove it, its a worthless item.

        1. Car batteries are made up of many sub units so that individual cell failures don’t make the whole thing unusable. When you have thousands of cells, you have to expect failures.

          Also, you need to provide some evidence for your doubts about life time. There is plenty of real world evidence from cars with hundreds of thousands of miles on them that show the batteries last at least as long as a typical petrol engine.

          1. These are vehicles like taxis that rack up the mileage in a short time, this is a very different use case to someone who commutes 10 miles a day or only does the shopping once a week, in 10 years time with 40k miles on the clock will the battery still be ok? Doubt it.

            I run a garage, taxis and fleet vehicles have a pretty easy life(the engines anyway) vehicles which are used spradically develop far nasiter propblems

          2. Are you kidding? These cars picked up 150k in under 3 years, with multiple rapid charges per day. Rapid charging is the most stressful thing for the battery.

            I don’t know why you think going easier on them for 10 years will be worse. Maybe other parts of the car will wear a bit more but not the battery.

            Anyway, early Prius and Leaf models are not showing major battery life issues. Show us some stats if you think otherwise.

          3. Refurbishing is the key. It should be an easy process. Take the battery pack, check the individual cells, replace the damaged 2%… and you are back to 100% for 300 bugs. Do it once a year from year 8-10 and done infinite battery lifespan. That should be the way to go.

      2. I’ve heard this before.

        There is a trend with many manufacturers to use so called “Lifetime” transmission fluids in their new cars. Audi, BMW and Mercedes have been doing this for years, Volvo more recently. The real question is what is a “lifetime”? If the lifetime of the car is the reference point, most owners will be sorely disappointed, as almost all of the fluids need service between 80-100K miles, far shorter than the lifetime of most European cars. While fluids and lubricants have doubtlessly improved over time, the real reason for these “lifetime” fluids is the extended service intervals of new cars.

        Often times the manufacturer will offer “free” service for the first 60K or so miles. So the “lifetime” fluid is just one way for them to lower their costs, you just pay the tab later. The program is great for the first 60,000 miles. The original owner will rave about the low maintenance car where they received 3 or so free oil changes & perhaps a brake service. A happy owner drives Consumer Satisfaction Scores up, more new cars are then sold and the manufacturer is very pleased. Problem is, the next 60,000 miles. If the original owner keeps the car, reality will set in pretty quickly, or worse, the car is sold, and now the new owner starts to pay the piper for the deferred service.

        Moving parts need lubrication and hot, wear prone metal on metal contact parts will accumulate debris and wear over time. Lubricants break down. Never changing out lubricant for 100,000 or 150,000 miles is antithetical to a well running car. But nobody wants to deal with the “hassle” of servicing their new car. But then things break down. Surprise, surprise.

        Batteries are not quite the same but I have yet to see one that does not lose it’s charge holding ability and also noteworthy, they do not do so linearly either.

        1. Tesla use Panasonic cells rated at 3000 cycles to 80%. Full range is about 300 miles, so 900,000 mile expected lifetime.

          Tesla’s tests suggest that is about right. Obviously some will have early failures, but there are quite a lot of Teslas with 300k+ on them and only minimal degradation.

          Head over to the Tesla forums and SpeakEV, there is loads of info and stats to look at.

      3. Mileage is not a good metric to gauge battery lifespan.

        Car battery packs die from several factors, all non-linearly dependent on time.

        Internal resistance of each cell increases, capacity of each cell decreases, balancing is basically abandoned cell by cell after five years, etc. It all results in a sudden drop off in performance, not just capacity.

        Sneaky EV designers increase battery lifespan by ‘quietly’ reducing USED capacity (from ~40-80% to ~40-70%) and throttling max power (to ~80% of new) output as the car ages. The reduction is considered tolerable and gives another few years.

        There are good, technical, reasons Telsa backed out of their optional “unlimited battery replacement” warranties.

        “Second-hand packs” will be cheap…. because they are mostly useless.

        “Replacement packs”, i.e. packs which can actually provide >80% of the usefulness of the original pack, will be expensive.

        That feels about right.

        1. Tesla’s unlimited mileage warranty is still in effect, go check their site. They offer 8 years and unlimited miles on the battery and drivetrain: https://www.teslamotors.com/sites/default/files/pdfs/Model_S_New_Vehicle_Limited_Warranty_201602_en_GB.pdf

          There is also no evidence that the oldest Teslas are losing performance or their batteries are suddenly starting to die after five years. Keep in mind that the Roadster started sales in 2008. The oldest Leafs are six years old and don’t exhibit the problems you predict or claim exist either.

          Back your claims up with some data or evidence.

      4. I have a leaf, mixed driving conditions, first 40k was highway long commute, next 15k was highway short commute, last 5k was sporadic use, I have lost aprox 15% of my battery capacity lost (3 bars of 12) I love electric car but it’s reduce range is killing me

        1. How old is it? You should be covered by the battery warranty it you drop another bar.

          The battery is so reliable that new models have dropped the 80% charge option entirely. I’d contact Nissan and at least ask them to check your battery out (they can do some diagnostics) because it seems like abnormal degradation.

      5. this is no different then led headlamps.

        i can’t find the article anymore, but within the last year or two, audi in europe had to replace a whole bunch of their led headlamps because they no longer met EU output requirements.

        at a bare minimum, all the led headlamp chips currently in use are rated for at least 30,000 hours, usually closer to 50,000 hours. led headlamps haven’t existed for all that long to even come close to those life spans, even if left on 100% of the time since leaving the factory.

        just because companies say things will outlast the car doesn’t mean they actually will.

      6. It is not appropriate to rate lithium-ion batteries for cars in terms of miles, instead do so in terms of time. As I understand it the chemistry of Li-ion cells means that they have a lifetime that is fairly fixed no matter how many miles you get from your car with them. Perhaps there will be a real Li-ion expert among the readers who can elaborate.

        It’s also worth pointing out that the dead batteries in the OP were lead-acid before declaring FUD.

        1. That’s incorrect. Lithium batteries are mostly limited by the number of charge cycles and temperature. For example, the cells that Tesla uses are made by Panasonic and rated for 3000 cycles to 80% remaining capacity at a 1C charge rate and given temperature. You can check various battery datasheets to confirm this.

          Life time has little effect, beyond the danger of over-discharge if left for too long.

  2. Should make a big improvement! There needs to be at least one new electric truck in production. When lead-acid was the only choice, trucks made the most sense for EV conversions since they had the space and suspension for the batteries. If the auto industry gave us a few more choices in EVs I think they’d get a lot more EV sales.

    1. It’s not about choice, but price.
      People are not going to buy $50k+ cars, if there are $30k ones (new), that have approximately the level of “luxury” items/utility.
      A truck needs to be able to carry load, the batteries will reduce that capability or turn it into an actual truck, which requires a different drivers license in most of the world and has legal restrictions that the pick-ups don’t have… What do you think people will choose, a truck that’s significantly more expensive, yet less usefull or the cheaper one with more carrying capacity and less problems?

      Automakers want profit, you can’t blame them for that. Developing said truck costs money and you need to sell quite a few of them to pay the production startup cost. If they figure they wont be getting their money back = no new electric trucks…

  3. “… there are taxi firms with Leafs on 150,000 miles and less than 20% capacity loss.”

    My 2013 Leaf had 20K miles last month and had 20% capacity loss as measured by Leaf Spy app.

    “Also, replacement packs won’t be too expensive.”

    Nissan sells replacement battery packs for the Leaf for $5500, providing you return the original battery pack.

    1. The price for used Leaf packs is hovering around $3000 +/- depending on mileage.

      I wish I got mine earlier when they where cheaper… ;)

      They do seem to be more hacker friendly than the Volt or Tesla modules, (well engineered and easy to configure into different voltage / amp-hour capacities, and don’t require liquid cooling).

    2. I’m a leaf owner too, 30k miles and about 5% loss n Leaf Spy. Degradation is generally non-linear.

      Your car seems to have issues, I’d take it to with Nissan. What country are you in? You seem close to a warranty replacement.

      Good luck.

  4. Battery Packs are influencing the used car market prices now. At least on the bottom end. You can buy a gas car, at the bottom of the market, for about $500-$1000. (such a car will almost certainly need work – and it depends on the owner, because it could be something simple and cheap like a $12 thermostat, or it could be expensive like new rod bearings or cylinder head). Just pointing out that you can REALLY “luck-out” if you’re clever, buying a used gas car. The inherent SCRAP value of such cars is usually about $150-$300 if you just drop it off at a junkyard. (in many cases, just the TOW charge will overwhelm any money you’ll make).

    On the other hand, the FLOOR of the used electric/hybrid car market is very stubborn – I’ve never seen one for less than $2500. This is because the inherent value of that used battery pack – even if it’s “dead”. Even if the rest of the car is completely f**ked. If I could get an electric/hybrid wreck, very cheap, like in the $200-$500 range, I would probably jump on it, as those batteries could be used in a conversion or repair of an existing electric car.

    Most DIY conversions aren’t going to hit anywhere near the performance of a Tesla. Not for that budget level, anyway. But I often fantasize about putting together an electric commuter for cheap $$ out of parts of a wrecked Tesla. Tesla performance without the overhead of having to be network-connected to Tesla’s servers and maintenance oversight.

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