Battery Longevity And The "80/20 Battery Rule”

Aptera Community Aptera Discussions Battery Longevity And The "80/20 Battery Rule”

Aptera Community Aptera Discussions Battery Longevity And The "80/20 Battery Rule”

  • Battery Longevity And The "80/20 Battery Rule”

     Jonah Jorgenson updated 3 weeks ago 14 Members · 22 Posts
  • Bob Minor

    Member
    June 8, 2022 at 1:57 pm

    (Fast charge happens between 20% and 80% battery capacity. Generally charge to 80% and try not to discharge below 20% battery capacity.)

    Looking from a battery longevity perspective, does it basically say that you have effectively 60% of your battery to use without potentially causing any negative change in the battery state of health? Or, Maybe only limit a DC fast charge to 80% ? This would totally change my thoughts on which battery to purchase on my Aptera.

  • Benjamin Dreidel

    Member
    June 8, 2022 at 2:23 pm

    Yes

    • Bob Minor

      Member
      June 8, 2022 at 2:49 pm

      Well that’s an answer I can understand 🙂

      • Konijnerd the Great

        Member
        June 9, 2022 at 8:00 am

        while true, don’t worry about it if you use the car a lot. then charging to 100% and discharging to 1% isn’t a issue(except that 1% is gonna be tight to find a charge spot)

        The 20-80% is for when you park the car and let it alone for a while, then it’s not great for the battery chemistry to be fully charged or drained.

  • Peter Jorgensen

    Member
    June 8, 2022 at 2:48 pm

    Correct. In real world practice a full range of 250 miles on most EVs produces a highway range of about 150 miles which is plenty for interstate travel in the US. It doesn’t sound like a lot but it’s a good amount. You can DC fast charge to 100% too if needed but it’s not super common. It’s just slower.

    More than that would be nice for special circumstances or for skipping areas of poor infrastructure easier. But realistically, modern DC fast charging is to the point (in the US) where you don’t need a lot more than that. 400 would be great and 600 would be just dreamy for long desert trips to non-ev saturated areas and places like Alaska.

  • Curtis Cibinel

    Member
    June 8, 2022 at 2:49 pm

    All charge/discharge will result in some degradation of any battery but if a vehicle can last 400,000 miles with 80% of its original capacity it shouldn’t be a big deal. People with experience with Teslas will attest to the fact that this issue is overblown.

    Staying in the mid range is good for commuting but you wont tank a battery by using the top/bottom a few times per month. Good data is available in threads discussing potential for LFP. Given the vehicle has enough space for a 100+ kwh pack it shouldn’t be hard to get a 400 or maybe even 600 mile pack into the vehicle and save substantially on cells per car. They need to get to market and that will be with the 2170 but eventually the cost/benefit of the transition (which will likely cost millions) should be examined. This would add ~150lb to the 400 mile pack (using readily available off the shelf cells) but would make the entire thing usable since the pack degrades about 1/3rd as much. This could also save thousands per car (batteries are a very expensive component).
    https://aptera.us/community/discussion/lfp-potential-for-bester-energy-density/#post-25836

    Note: Safety and lack of cobalt are two other great reasons for LFP.

    LFP potential for major energy density improvements

    • Bob Minor

      Member
      June 8, 2022 at 2:58 pm

      Granted with any battery any charge and discharge cycle will cause some level of damage, is there an actual standard for what a “charge cycle” actually is. For me, plugging in at home after a round trip commute is a charge cycle but the solar panels charging as it sits in the parking lot at work so to speak is not really a charge cycle. Does that make sense? Im kind of getting battery nerdy here, but I have a very long commute now and it appears Im on the edge of a 60Kwh and 100Kwh battery pack.

      • Benjamin Dreidel

        Member
        June 8, 2022 at 9:15 pm

        As I understand it, a charge cycle is a full charge. For example, if you charged 10kw each day for 6 days on a 60kwh battery, that would count as one charge cycle. For a 40kwh Aptera, 1000 cycles would be 400,000 miles.

  • Matthew Manzi

    Member
    June 8, 2022 at 9:22 pm

    So yes, NMC batteries do better when between 80 and 20 percent of charge. If you stay there most of the time you will get more life out of them. The thing that most people get wrong is they think you always need to stay in those ranges. NMC chemistry batteries are fine being fully charged, they just don’t like sitting for long periods at a high state of charge or being hot while fully charged. It’s completely fine to fully top off your battery before leaving on a long trip as this will have negligible effects on degradation. Also these cells are rated for 1000 full discharge cycles which is about 300 to 400k miles on the 41kwh pack. That’s more then you can expect out of the rest of the car so no real reason to baby the battery too much. Aptera should also fair better then most EVs as its so efficient that it will produce minimal internal heat unless you are testing the 0 to 60 constantly. Really the big killer of batteries is keeping at 100 percent charge in very hot climates for long periods. If you just avoid that you should be fine.

    • John Wiley

      Member
      June 9, 2022 at 6:51 am

      How about the effect of draining the battery to below 20%, say, down to 5%? This would probably easily occur on a long road trip.

      • Peter Jorgensen

        Member
        June 9, 2022 at 7:09 am

        In my experience this is pretty uncommon – I usually don’t go below 20% on road trips – I target 20 and usually come in at 25-30% SOC. If you have some sort of problem and need to dip into that reserve then you can – I’ve gone down to 16% once.

        • John Wiley

          Member
          June 9, 2022 at 7:12 am

          My question is would draining below 20% do any significant damage to the battery?

          • Joshua Rosen

            Member
            June 9, 2022 at 7:34 am

            Charging dropping below 20% isn’t terrible, what you don’t want to do is drop it to 0 but even then it won’t kill your battery unless you do it frequently. These rules are about maximizing the batteries life, with best practices a battery will last 1000-1500 cycles before it loses 30% of it’s capacity. With poor practices that number is more like 500 cycles. Note that these are just the commonly quoted numbers. The actual numbers for each particular cell will be different and presumably they will be getting better as battery designs improve.

            During the week I keep my battery charged to 75%, that gives me about 200 miles of range in my Model 3 which is more than enough for local driving. When I do a road trip I’ll charge up to 90% just before I leave. I frequently get down to 15% at the end of those trips but I usually pull into Superchargers at a higher level than that because I like to have a lot of margin. I’ve reserved the 600 mile Aptera, I’ll keep it at 50% during the week because that’s supposed to be the level where batteries are happiest. On road trips I’ll charge it to the level that will allow me do the whole trip without DC charging. I’ve picked the 600 mile version because the absolute longest trip that I do in a day is 450 miles and I believe that the 600 mile Aptera can do that especially since half the driving on those trips is back roads. The vast majority of my trips are about 350 miles which the 600 mile Aptera should be able to do without breaking a sweat.

          • David Marlow

            Member
            June 9, 2022 at 7:38 am

            The Issues out side of the 80/20 rule is the rate of charge/discharge, the temp of the battery and how well balanced the cells are in the pack. Being careful about all of those parameters the battery should last over 10 years even if cycled every day. The main deration of the battery will be due more to time.

            The normal recommendation to replace the battery is when the total capacity is less than 80% of new, however it can usually be safely used until it falls below 60%. At that point cells will start to short out.

          • kerbe2705

            Member
            June 9, 2022 at 7:50 am

            @John Wiley All EV battery management systems allow for a buffer at the top and the bottom of the pack capacity: The problem is that advertising usually states the nominal capacity of the pack, not the useable capacity. When you charge your EV to “100%” there’s still some excess capacity above that so that you can’t “over-charge” and the same goes for the other end: The car’s “range guessometer” may say that you have 0 miles of range and the vehicle may stop moving but there’s still some hidden capacity to protect the cells.

            My PHEV, for example, has a nominal 17 kWh battery pack – but can access only 13 kWh.

            • Joshua Rosen

              Member
              June 9, 2022 at 8:31 am

              The buffers on PHEVs tend to be a lot bigger than the buffers on BEVs. Because of the small battery on PHEVs the normal operation is to always charge to 100% and then to run them down to 0% where the engine kicks in. I had a Volt which had an 18.4KWh battery, 14KWh was usable, I saw no battery degradation in the three years that I’ve owned.

              With BEVs the buffer size is dependent on the manufacturer, it looks like Ford put huge buffers in the Mach-E and I think Audi is also conservative, in both of those cases they assume that their customers won’t understand battery management. Tesla exposes much more of the battery to the customer because this allows them to claim a longer range. Tesla does maintain a 15 mile buffer below 0 but they’ll let you use it so it’s there to keep you from running out of energy rather than to protect the battery. It looks like Aptera will be more in the Tesla camp, the reports are that the 400 mile version will have a 44 KWh battery, 40KWh usable. Because the range on most of the Aptera variants will be so large it will be easy to use good battery management practices without any inconvenience. Only the people with the 250 mile version will faced with making any tough decisions about range vs battery life. If you have the 400 mile version just set it to 60% most of the time and then set it to 90% when you do a road trip. If you have a really long leg on a road trip then doing 100% is OK.

              As for roadtrips, the one area where the Aptera will be deficient is DC charging, they are only promising 60KW which will be terrible if you have to do a full charge. However it will be fine for stretching out your range. My Supercharging stops usually just add about 100 miles at a time, we stop long enough to go to the bathroom and in that time you can get 100-150 miles in a Tesla. Because the Aptera is so efficient you’ll only need 10KWh to go 100 miles, even with it’s low DC charging rate it should be possible to get that in the same 15 minutes that it takes with a Tesla.

  • Russell Fauver

    Member
    June 9, 2022 at 2:02 pm

    80/20 rule is interesting. On a hundred mile per charge vehicle you’re down to about 20 miles at 20% which might get one a bit nervous about finding a charging station. On a thousand mile vehicle like the top spec Aptera there’s still 200 miles left in the pack. I probably wouldn’t be concerned about dipping below 200 miles remaining. If 100% charge gives thousand miles of range and one thousand charge cycles will degrade the pack to 80% capacity, the vehicle would have traveled almost 1,000,000 miles. Plus, after a million miles of driving the single charge range would be reduced to ‘only’ 800 miles. In this case 80/20 charging hardly seems worth the bother.

    • M T

      Member
      June 9, 2022 at 4:06 pm

      Battery life is interesting, there are few studies out there now for NMC EV grade batteries. Most agree you get 800cycles to 80% capacity. That’s for the full monty, 100%-0%. Apetra won’t let us deplete below 10% of real capacity, so lets use a conservative 850 cycles. For the 400 mile battery that would be 340 000 miles. At that point he battery is not a boat anchor, it’s a 320 mile battery. If you follow the 20-80 rule you can basically double that. so 1700 cycles, , but your cycles are now only 240 miles. Still that is a better 408 000miles to 80% capacity. That’s a lot of driving.

      The above is an oversimplification as other factors will affect you long term battery capacity: pure age, storage and charging temperature, and the use (or not) of DC fast charging. On average EVs have reported a 2% decrease in capacity per year. That includes Nissan leafs, so we will likely do a bit better, but still, you can count on 10 years to 80%.

      https://www.chargedfuture.com/electric-car-battery-degradation/https://www.chargedfuture.com/electric-car-battery-degradation/

      After reading the above I will try and limite my DCFC use. The good news is it seems if you only charge to L2 or lower rates, you can basically drive 34-40k miles a year for 10 years without having a significant impact on your battery capacity.

      • Russell Fauver

        Member
        June 9, 2022 at 9:36 pm

        Agreed. It seems that for most drivers the batteries will age-out before charging style would have any meaningful impact.

  • Tim Dean

    Member
    June 9, 2022 at 4:35 pm

    So, how many batteries are in the 40kw pack?

    https://youtube.com/shorts/yGDkiUAwxRs?feature=sharehttps://youtube.com/shorts/yGDkiUAwxRs?feature=share

    Seal the pack well.

    • This reply was modified 3 weeks, 1 day ago by  Tim Dean.

  • Bob Minor

    Member
    June 9, 2022 at 4:55 pm

    My take away is 80/20 is then a best practice, but I wont be killing the battery if I top it off now and then for a long trip. On the 100Kwh battery I would have a 100 miles and change at 20% in a somewhat real world condition.

    Does that sound right?

    • Jonah Jorgenson

      Member
      June 10, 2022 at 6:02 am

      A good, rational, approach👍

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