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Protecting battery life in a modern EV

  • 24-11-2021 12:40am
    Registered Users Posts: 1,416 ✭✭✭celtic_oz

    Have an EV where the manufacturer recommends keeping the charge between 20% - 80%

    For the sake of illustration if you started off with 80% charge and used 10% every day, which is better for the battery :

    Charge every day from 70% back to 80%

    Leave for 6 days then charge once from 20% to 80%

    Or some other strategy ?


  • Moderators Posts: 12,309 ✭✭✭✭Black_Knight

    Charging (cycling) mid state with small depth of charge (10%) should be better for the battery. Maybe not 70-80%, but keeping the car around 50% seems better for longevity.

    For example, of you consume 2000kWh per year in your car, you're better off charging it more regularly at mid SOC than charging in less frequently to 80%.... The opposite of what I do basically.

  • Registered Users Posts: 77,955 ✭✭✭✭Atlantic Dawn

    80 to 20 and recharge would make much more sense.

  • Registered Users Posts: 11,849 ✭✭✭✭KCross

    In the example provided I dont think you'd notice any major difference with either strategy. At least not in the lifetime of the car.

    You could maybe argue that charging once a week is better as its less wear and tear on the various connectors and contactors in the charge point and the car, but even that shouldnt matter.

    Go with whichever strategy suits your needs.

  • Posts: 2,799 ✭✭✭ Marco Salmon Belly

    If the manufacturer says only use 60%of the battery, then the range is pathetic unless you violate the advice

  • Registered Users Posts: 11,849 ✭✭✭✭KCross

    The advice from the manufacturers isnt exactly that.

    It's usually along the lines of "keep it between 20-80% as much as possible, but charge to 100% as needed".

    So you have full access to the battery range/capacity but they dont want someone charging it to 100% and then going on holidays for a few weeks or having it at 100% everyday and only doing short journeys and then topping it back up to 100% again.

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  • Registered Users Posts: 1,069 ✭✭✭manonboard

    I think there has been some well published studies that although the common advice between 20-80 helps, its effects are very very minimal on modern day batteries. So much work has been put into removing the constraints that its all a bit outdated. It still helps, but its very minimal.

    Same with fast charging v slow charging.

  • Registered Users Posts: 20,182 ✭✭✭✭ELM327

    Your battery BMS will not allow you to access the very top or very bottom of the battery.

    Plug in and charge, drive, rinse and repeat.

  • Moderators, Sports Moderators Posts: 17,891 Mod ✭✭✭✭slave1

    Stop overthinking, don't leave real low or real high -10% +90% for extended period, that's it as ELM327 said

  • Registered Users Posts: 18,892 ✭✭✭✭Cyrus

    My car has a large buffer already built in and low range comparitively, we also do pretty low mileage, it gets charged from 10-15% to 100% once a week on average.

    Given that i wont have it longer than 3 years it doesnt matter that much to me, and its charged on AC 99% of the time anyway.

  • Moderators, Sports Moderators Posts: 17,891 Mod ✭✭✭✭slave1

    That's another myth, there's Leaf's and Tesla DC charged for years on end with virtually no difference in battery health compared to predominately AC charged vehicles. The BMS takes care of things...

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  • Registered Users Posts: 1,416 ✭✭✭celtic_oz

    I dont intend to leave low or high for any amount of time .. but I do have a tendency to charge to 80% frequently "just in case"

    It occurred to me that batteries have a set number of cycle times and was wondering if charging by 50% is equivalent to charging by 10% five times while also staying away from too high and too low.

  • Registered Users Posts: 11,849 ✭✭✭✭KCross

    Tesla DC charged for years on end with virtually no difference in battery health compared to predominately AC charged vehicles

    Really? I find that hard to believe. Arent there loads of examples of Tesla's being nerfed after X amount of DC charging to protect the battery. Surely Tesla wouldnt do that to its customers if there wasnt a real impact to battery health?

    I think its widely accepted that alot of DC charging has a negative affect but it does need to be alot to cause it.

  • Registered Users Posts: 1,361 ✭✭✭cannco253

    I wonder how Hyundai/Kia are managing this with the 800v systems they have in the Ioniq5 and EV6.

    Outside of Ionity and Tesla superchargers there aren't any options here to utilise it, but it would be interesting to see over the course of the next year or 2 how batteries in mainland Europe cope with the high speeds.

  • Moderators, Sports Moderators Posts: 17,891 Mod ✭✭✭✭slave1

    I usually agree with you but I this instance I think you are slightly off.

    Tesla nerfed the 85 battery pack due to battery pack failures not degradation issues

  • Lithium batteries don't like to be at high states of charge indefinitely, so as long as your not keeping it at 80+ regularly you should be fine, same at the low end. When you need full charge charge to 100% and forget about it.

    I didn't baby the BMW i3 94Ah i3 battery but it was never at 80+ for long and it still had the same range as when I got it and it was 4 years 7 months old and had 134,000 Kms I really didn't notice any range loss at all it was incredible!

    The main thing about the BMW i3 94ah battery according to the specs of the Samsung cells was the incredible cycle life and for such a small battery it sure was incredible and it will probably be good for many more years to come.

    The difference with the large batteries especially the 77 Kwh iid3 is that cycling will be a lot less than on the BMW i3 much smaller battery so in theory should last a very long time "in theory" but all to do with how robust the chemistry is more than anything.

    I do believe VW are being very conservative with the charging curve for such a large battery, I don't believe that having it hold 125 Kw until 60% at least would be detrimental as long as it's kept within spec and temperature kept low enough but at the same time fast charging a Tour or Tour 5 would be rare enough for me.

  • Registered Users Posts: 10,017 ✭✭✭✭the_amazing_raisin

    Personally I tend to charge when I go to around 30%, anything less and I feel that I don't have enough range for any unexpected journeys that are likely to come up

    I've got the limit set to 80% but my car doesn't see a lot of mileage since I'm WFH these days (long may it continue), but if I'm doing a long trip then I'll just set the limit higher the night before and charge to full