Why shouldn't I charge my 64 kWh Kona EV to 100% every day?

Discussion in 'Hyundai Kona Electric' started by JSU, Apr 10, 2019.

  1. JSU

    JSU New Member

    Tesla clearly discourages its customers from charging their batteries to 100% unless you are going on a longer journey that requires the extra range. But I do not see any sort of warning/advice from Hyundai about this. I've set the charing limits to 80% (I've never tried charing to 100% yet), but do I really have to? I had a 2017 BMW i3 and I charged to what I believed was 100% all the time, but I had been told that the i3 auto manages and protects it's battery as needed so there's no problem with going to 100%.

    Does anyone know if anything like this is documented for the Kona's battery? Am I prolonging the life of the battery by constantly only charging to 80%? Or am I just chopping off 50 miles of range daily for no reason.
    Gasfree4me likes this.
  2. I guess the question is really if you need those 50 miles or not. If you don't, you're just playing it safe.
    If it inconveniences you, I don't think there wouldn't be any reason not to charge higher. I charge mine to 90%. Not on a daily basis, though.

    Sent from my moto x4 using Tapatalk
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  3. davidtm

    davidtm Active Member

    I've read that a real complicating factor in this decision is that manufacturers differ on what they report as the battery capacity. That is, I believe that in a Tesla, 100% is really 100%. Other manufacturers, on the other hand, build in a "buffer", so that an indicated 100% is actually less by some variable amount. The same can hold for the bottom end of state of charge, as well.

    I would welcome any factual substantiation or disputation of this that exists!

    I would like this to be somehow standardized, so that we consumers don't have to do detective work about it.
  4. KonaTom

    KonaTom Active Member

    I heard that the kona ev has a 69 to 70kwh capacity. So it has a buffer too.
  5. The dealer told me to only charge it up to 80% when I bought the thing. I read another article someone posted on this forum recently that if you keep the charge between 20% and 80% at all times, you can get up to 3,000 discharges off the battery before they're toast as opposed to the ~1,000 times it can discharge if you charge it up to 100% all the time. That article wasn't Hyundai specific but it was about EVs in general. So I took that as enough evidence to only charge it up to 80%.

    Put another way, if you put an average of 20,000 km/year on your car and at 100%, you're getting the advertised 415km of range, you're charging it up 48x per year. That would mean the batteries should last almost 21 years. But you might start to see performance drop-off happen a lot sooner than 21 years.
  6. I'll gladly take the 415,000 km @100%:)
    navguy12 likes this.
  7. brulaz

    brulaz Active Member

    The 20-80% rule is generally for all Li batteries not just EVs. Some stretch it to 10-90% or whatever.
    But, as noted, if you stretch it too far, the number of battery charge cycles can be reduced dramatically.

    It seems to me that for battery warranty the EV manufacturers would use their charging software to keep the batteries within some reasonable limits.
    And the reported EPA range would reflect these limits. To rely on the user to do this "manually" is nonsense.

    Does Tesla or Hyundai really tell it's owners to limit their charge to 80% as much as possible to preserve battery life?
    Is it in the manual? Not sure if I would believe what a salesperson says.
    Last edited: Apr 11, 2019
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  8. JSU

    JSU New Member

    I sat in my friends Model 3 and I recall the screen clearly saying something to the affect that you should only charge your car to 100% only if the extra range is needed for that particular journey. I think that was in the Model 3's charging limits configuration screen on the display as a warning if you set the charge limit to 100%.

    Now in the Kona Electric owners manual, I do see the following paragraph in the "Electric Vehicle System Overview" section under "High Voltage Battery (lithium-ion polymer)":

    "If the vehicle will not be used for an extended amount of time, it is recommended to fully charge the vehicle to 100% before storing, and then charge the vehicle periodically (approximately every 3 months) to prevent the EV battery from dis- charging completely."

    This is the first time I've heard of actually recommending to charge to 100%. Even though its only talking about storage of the car and not the normal driving of it.

    I am hoping that there IS some sort of built in buffer for protection, but I think I'll stick to regularly charing to 80% since my normal daily driving doesn't normally exceed 50 miles anyway.
  9. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    All EV makers, including Tesla, hold some some fraction of the full battery capacity in reserve, so the usable capacity is always less than the full capacity. However, it may be that what Tesla reports as the battery capacity for the Model 3 is actually the usable capacity rather than the full capacity. Some claim that the Long Range Model 3 full capacity is 80.5 kWh, while the usable capacity is 75 kWh.

    But if so, I don't think Tesla has been consistent on that. Other reports indicate that with the Model S/ Model S battery packs, the name-plate capacity (60, 75, 85, 90, 95, or 100 kWh) is the full capacity -- altho rounded off to the nearest 5 kWh -- rather than the usable capacity.

    * * * * *

    But to address your question, the best practice for all BEVs using li-ion batteries (and all BEVs in production today use li-ion batteries) is to charge to no more than 80% (usable) capacity for everyday use. That is, 80% of what the car's instrument panel says is 100% charge, which will be the usable capacity and not the full capacity.

    Charge to 100% of usable capacity only when you expect to test the limits of your BEV's range, such as when planning on a long trip. There's no reason not to use 100% of usable capacity when it's needed; just don't do it every day if you're planning on keeping the car for more than just a few years. Charging it to 100% daily, or draining it to near 0% daily, will age the battery pack prematurely.

    Please note this applies only to BEVs. Best practice for PHEVs, which are engineered differently, is to fully charge them whenever possible.

    navguy12 and eastpole like this.
  10. brulaz

    brulaz Active Member

    Where does this "best practice" come from?
    I would have thought EV manufacturers would build that into their charging schemes.
    To say that an EV has a certain max range (but you shoudn't use it every day by charging to 100%) is rather deceptive.
  11. I read the manual and to me it seems to suggest charging past 80% is worse when charging via DC Fast than AC. I charge level 1 AC most of the time and plan to charge to 100%. But if I use DC Fast on a longer trip, I plan to only charge to 80% (and I set the limit at that in the car settings). Besides, the battery pack has a lifetime warranty, right? I mean "worst case" scenario you get earlier degradation of the charging capacity .. say at 8 years instead of 10 or 12 or 15. Well... then the warranty kicks in.

    Summary: on AC power I plan to charge to 100%. On DC Fast, 80%.
  12. Ya, this battery stuff reeks of wive's tales and urban legends. Just charge it and forget about it.
  13. brulaz

    brulaz Active Member

    Wonder if that "extra" range is beyond what they advertise. But I doubt it. The model 3's range per battery kWh are higher than anybody else's and maybe pushing the batteries limits is one way they do it (in addition to their fine engineering of course:D). Perhaps the Koreans and Germans (Audi?) are more conservative.
  14. The model S and X definitely have some extra capacity. Remember when the hurricanes stuck Florida and Tesla unlocked extra range in the cars for people to get out?

    Sent from my moto x4 using Tapatalk
  15. brulaz

    brulaz Active Member

    Do you recall the exact wording in the manual?

    There's a chart around here from FastNed a Dutch charging company that shows once the Kona battery reaches 70% on their DC fast chargers, the charging rate drops off dramatically. To ~38kW @ 72-77%SOC, ~25kW @ 78-87%SOC, and then tapering off to 10kW at 95%SOC.

    So the Kona reduces the DC charging rate at high SOC, presumably to preserve the battery.
    Folks may just charge to 80% SOC because it gets so slow after that, not because it's necessary to protect the battery.
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  16. In the past I charged up to 78% at 48kw at a 50kw charger. At that point it started to reduce the charge rate.

    Sent from my moto x4 using Tapatalk
  17. No but I looked it up:

    Charging Information • Level 2 AC Charging : You can charge your vehicle using a 240-volt AC electrical EV charger in your home or at a public Level 2 charging station. • DC Fast Charging : You can charge your vehicle using a DC fast charger with a compatible charge cable at a public EV charging station. Make sure that the station has a compatible connector for your vehicle. Note that prolonged and continuous use of DC fast charging may reduce the long term life of the EV battery. Usage of a DC fast charger should be minimized when possible in order to help prolong the life of the EV battery. • Level 1 AC Charging : The Electric vehicle can be charged by using household electricity. The electrical outlet in your home must comply with regulations and can safely accommodate the Voltage / Current (Amps) / Power (Watts) ratings specified on the portable charge.

    Additionally, there's a table that basically says Level 1 / Level 2 take x hours when charging to 100%, but in the table for DC fast it specifically says: "Takes about 54 minutes at room temperature when charged to 80%. Can be charged to 100%."

    Now I'm reading between the lines a bit I suppose. But to me, I take this all to summarize as: "It's best to charge using AC, and charging to 100% is fine on AC. If you charge on DC, it's best to charge to 80% but you can charge to 100% too, but whether you do 80% or 100% it's best not to use DC fast a lot, if possible. AC charging is best in general" ​
  18. KonaTom

    KonaTom Active Member

    Yes. Hyundai has built in safeguards.
  19. brulaz

    brulaz Active Member

    Thanks for that.
    Just not sure about "best to charge only to 80%" on DC fast chargers.

    The highest rate of DC fast charge (~75-80kW?) occurs at the lowest %SOC,
    Dropping to ~10kW at 95%SOC. That's not much different from a level 2 AC charging rate.

    So another interpretation is that the high rates of charge at lower SOC are detrimental to battery life, but topping up to 100% at the lower rates of charge is just slow. In practice, it is prolly best to plan on just doing ~80% on fast charge anyway, unless you have all day and nobody else needs the charger. :)

    Don't some DC fast chargers cut you off at some point if you're charging too slow?
    Mattsburgh likes this.
  20. I said "best to charge only to 80% on DC fast" more for the money and time issue than anything else. (But certainly seems possible if not likely that stopping at 80% is also a bit better for the battery)

    But my main reason for setting mine to 80% for DC fast is that I assume if I'm using DC fast I'm traveling and I'm in a hurry so if I can get 80% in 54 minutes, but another... half hour only gets me, say, another 10%, I'd rather stop at 80% and drive 200 miles and then charge up to 80% fast again, rather than try and top off above 80% at what would be considered a trickle comparatively.
    electriceddy, Esprit1st and brulaz like this.

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