EV / battery charging question

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Batman

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#289907 7-Oct-2021 17:27

I keep my phone charged between 20-80%.

I recently read you should keep your EV charged between 25-75%. That means you only have half the range you paid for!

Anyway - let's say you have an Older EV and its battery is now only 75% SOH.

QUESTION

What's the point of charging a 75% SOH battery to 75% - if you charge it to max you are really charging it to 75%.

Is there any advantage in terms of reducing further battery degradation by charging a 75% SOH battery to 75%?

RUKI

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#2791541 7-Oct-2021 23:13

I charge my phones, laptops and my car to 100%.
Batteries in Blackberry, Nokia and Samsung Smartphone outlived the phones...

I saw however that some people do not even know what % stands for and tend to believe they give their job 100%:
20% on Monday, 20% on Tuesday...... 20% on Friday ;)

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mkissin

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#2791549 8-Oct-2021 03:45

That's largely older advic now. Most EVs won't care if you charge them to "100%"

The older Nissan leafs saw increased battery degradation if they were left at 100% for extended periods of time. Since their batteries started small and tended to degrade somewhat quickly anyway (mainly due to the lack of thermal mangement), the advice was to not just leave them sitting at 100% charge for several days. Charging them to 100% and immediately using them isn't an issue.

It's a nuanced issue, but in general, don't worry about it. Use your car how it suits your life.

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#2791553 8-Oct-2021 06:37

I charge my phone to 80% most of the time, AccuBattery tells me after about 15 months use the battery is still at 98% of capacity. With a car if you don't need the full range maybe you could see if the car features let you set a maximum charge, but if you need it, you need it, charge it up.

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#2791572 8-Oct-2021 08:01

It depends on the EV in question.

None of them say dont charge to 100%, but for most of them leaving them charged at 100% for long periods can harm the battery. Likewise you're not supposed to leave them at below 20%, but again you can use them under 20% but just make sure you charge them once done.

So day to day you charge to 80-90%. thats 400km+ in mine and I do ~40km a day. Not a big issue.

Now this depends on the EV itself and the chemistry of the battery.

The SR+ model 3 uses LFP cells (instead of NCA) and you are recommended to charge these to 100% at least once a week, you can use all that battery all the time. Its a much better chemistry ( more robust, cheaper etc) but its less energy dense and heavier.

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#2791583 8-Oct-2021 08:46

But if the battery SOH is 75% then charging to 100% is only charging to 75% no?

mkissin

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#2791590 8-Oct-2021 08:55

Not really. Think of it as slowly filling a petrol tank with sand. That portion of the tank is filled but unavailable to you as energy. So a reduction in SoH reduces the battery size, it doesn’t leave some of it empty.

It’s a poor analogy in many ways, but kinda works.

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RobDickinson

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#2791591 8-Oct-2021 08:57

100% is a particular voltage, you charge to that voltage at whatever SOH, the energy stored in the pack is different though.

1101

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#2791607 8-Oct-2021 09:35

unless you know the ACTUAL voltage per cell, youre making assumptions

Is 0% really 0v , or is 0% 2.8v-3v : the lowest ~safe~ voltage
What is 75% . Is that 75% range or 75% of MAX voltage ?

A car charging circuit & battery management circuit is smarter than a driver . Let it do its job ?

Generally , lithium batts loose life if left in low charge or constantly drained too low .
You could be better to keep it near fully charged , than say 75% and then run it too low too often .