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Discussion Starter #1
Hi there

I have a 2015 i3 and am trying to get the car to finish charging at 80% by setting an appropriate off peak charge window in the middle of the night. At that time to take advantage of off-peak tariff. And 80% as that’s supposed to be better for the battery than 100%.

It starts charging off peak. But regardless of how short I set the window, it fails to stop charging at the time I’ve asked it to, so when I wake up it’s always at 100%.

any ideas?

many thanks!
 

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Discussion Starter #4
thanks - I’ve got a 18kWh battery and a 7kw home charger. So I’ll set the charging times in the settings on the car menu from 1am - 2am for instance, or 1am - 130am, but it’s always full when I look in the morning.
Realise 80% precisely might not be possible, but not so bothered about that - I’m just trying to get to less than 100%
 

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My understanding is that the battery management system handles the benefits of charging to 80%(by never charging to the full 100% the battery is capable of). So I just charge it to 100% when I have off peak or solar power available.
 

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My understanding is that the battery management system handles the benefits of charging to 80%(by never charging to the full 100% the battery is capable of). So I just charge it to 100% when I have off peak or solar power available.
This is correct, BMW have built that into the car with the BMS, just charge to 100%.
 

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As has been pointed out on another thread (by Lexden and others) it is generally accepted that not charging to 100% will extend the life of the battery pack. This equates to not charging to 4.2 volts per cell as I understand it. It is quite likely that the car’s BMS (Battery Management System) actually limits the voltage to a lower value (maybe 95%?) but the EV manufacturers are quite coy about declaring this kind of information so most of the evidence comes from the battery manufacturers or “second hand” anecdotal evidence.

In general, battery life seems to be quite a bit longer than originally expected, perhaps several 100 thousand miles, but again it is difficult to get firm data. If this is the case then for most people there is really no need to be too cautious with charging.

Unfortunately there is no simple way of partially charging other than to physically stop the charge before 100%. That becomes impossible if you are tariff charging.

I can see that manufacturers might be reluctant to have charge timers in the car as this would send the wrong messages to the market place i.e. if you do what’s best for the battery you will limit the range. Not what people want to hear.
 

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Unfortunately there is no simple way of partially charging other than to physically stop the charge before 100%. That becomes impossible if you are tariff charging.

I can see that manufacturers might be reluctant to have charge timers in the car as this would send the wrong messages to the market place i.e. if you do what’s best for the battery you will limit the range. Not what people want to hear.

What manufacturers? All Teslas have charge limit (%) setting.
 

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What manufacturers? All Teslas have charge limit (%) setting.
Well, they’ve got bags of range to spare. I didn’t say all manufacturers. Just making the point that if you have an EV with 160 miles range and then say it’s better to charge to 90% then you are effectively marketing a 145 mile car.
 

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For standard charging I wouldn't worry too much die to BMS. For rapid charging, it's a different story and doing this repeatedly will probably shorten the battery longevity especially if you take it higher than 80%. Also repeatedly dropping the charge to below 20% will shorten it's lifespan.
 

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For standard charging I wouldn't worry too much die to BMS. For rapid charging, it's a different story and doing this repeatedly will probably shorten the battery longevity especially if you take it higher than 80%. Also repeatedly dropping the charge to below 20% will shorten it's lifespan.
What would you call a rapid charger, is it a 7Kw or do you mean the 50kw one’s, that charge in about an hour or so?
 
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