Zugzwang
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Battery Management Strategy

Tue Apr 24, 2018 6:28 am

A newbie question on how to treat your EV battery:

With some rechargeable batteries for common household items, I have seen that the user manuals recommend that rather than constantly charging, it is better to let the battery run out and then recharge it back to full. (I have no knowledge if this true or a myth, but I've read it a few times now).

I had originally planned to just plug in my future LEAF daily overnight and keep topping it up. Is that a poor strategy? Is it better to wait for it to run down and then give it a "full" charge?

Or does it even matter? Do you waste electricity if a fully charged battery is plugged in? Is that harmful to the life of your battery?

(Apologies if this already covered in another thread, I wasn't able to track it down)

Thanks for your thoughts on this!

WetEV
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Re: Battery Management Strategy

Tue Apr 24, 2018 7:30 am

Zugzwang wrote:A newbie question on how to treat your EV battery:

With some rechargeable batteries for common household items, I have seen that the user manuals recommend that rather than constantly charging, it is better to let the battery run out and then recharge it back to full. (I have no knowledge if this true or a myth, but I've read it a few times now).

I had originally planned to just plug in my future LEAF daily overnight and keep topping it up. Is that a poor strategy? Is it better to wait for it to run down and then give it a "full" charge?

Or does it even matter? Do you waste electricity if a fully charged battery is plugged in? Is that harmful to the life of your battery?

(Apologies if this already covered in another thread, I wasn't able to track it down)

Thanks for your thoughts on this!


Different types batteries need different care for best life.

The Li-ion battery in the car is best to keep between 20% and 80% for best life.

So just plugging it in will charge to 100% and keep it there. This is a poor strategy for long battery life, as far as I understand it. There are several alternatives to consider:

1) use a timer to charge to 100% before departure. Plug in when you get home, and the car will charge when the timer allows.

2) use a timer, and charge for some amount of time. Plug in when you get too low, and unplug the next day.

I do both. I have one timer set for an hour, and as I typically use less than 6kWh per day most days, I'll plug in if below 50%. I have another timer set for about departure time for a longer trip. I plug in, and the car doesn't charge until a calculated time before the departure time entered.

A reference:

http://batteryuniversity.com/learn/arti ... _batteries
WetEV
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flydiver
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Re: Battery Management Strategy

Tue Apr 24, 2018 8:15 am

That's OLD info and only relevant to old Nickel chemistry. Modern NiMh batteries "may" benefit from a cycle once in awhile but generally not. Just charge them when they get low. Don't leave modern LSD-NiMh in a trickle charger.
A lot of the info you get off the web about batteries is poor, especially from self-proclaimed experts.

Lead acid batteries prefer to be fully charged, all the time. Full discharge is very bad for them.

Lithium ion is a whole different chemistry. +1 on what WetEV said.
Try to keep it between 20-80%. Fully charge if you need it, but try to not have it sit fully charged for long....especially if it's hot. Full charge + heat = battery degradation. Very low is also not good, along with anxiety producing. When my wife got her first low battery warning she kind of freaked, even though she was only a few miles from home and had plenty of reserve left.

How you do that is up to you and your use pattern. If your use is predictable (regular commute) and your Leaf has charge-timer option you can likely set that. If not you'll need some other mechanism.

I've had mine about 6 weeks now and am getting more used to what I do with it, how long the battery will last, and how much charge I put back in a given time frame. (big improvement when I got 220v). My schedule is completely random (retired) so I haven't found the integrated timer of much use. I just try to keep 'enough charge' but not 'too much' and err on the positive side.

This is a good source for decent battery info.
http://batteryuniversity.com/

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Nubo
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Re: Battery Management Strategy

Tue Apr 24, 2018 10:55 am

The recommendations for fully cycling Lithium batteries are not for the benefit of the cells, but for the battery control software. Estimating the real capacity of a battery is something of an art, combining multiple data points. A full cycle can give additional data to help the software calibrate its estimate of capacity. I believe this is why you'll see such advice from computer and smartphone manufacturers.

Keep in mind their goal is not maximum battery longevity but rather customer experience -- they want the capacity-remaining estimate to be as accurate as possible so that the customer who is counting on that last 2 percent of power, is not surprised by a sudden shutdown.

Laptop and cellphone batteries are cheap enough to where it can make sense to trade ultimate longevity for a little extra accuracy. For a $6000 car battery, the sweet spot moves more towards longevity. The advice to generally stay between 80% and 20% is good. It can still be helpful to occasionally go through a large cycle. In particular, leaving the car on the charger to 100% and then an additional few hours gives it a chance to top-balance the cell voltages. This can make a significant difference in the accuracy of the car's capacity estimate especially at the low end.

Keep in mind the concept of "100%" is an abstraction. There's no real absolute. Well actually there is -- when the cell begins to deform, vent or catch fire. The cell manufacturer will specify a particular voltage as "100%", but that is somewhat arbitrary to begin with. The device manufacturer (in this case Nissan) will then further restrict the range both at the top and the bottom, to further preserve the cells. So there is some padding at both ends even if you drive from "consumer 100%" to "consumer 0%".

That being said, I'd still recommend against running the car dead flat. For one thing it's rather inconvenient, but also hard on the battery. I try to avoid "turtle mode". Occasionally I will get the VLBW (very low battery warning), which is probably not that bad as long as the car is charged soon after. Which gets to the point of time-spent at the extremes. Charging to 100% then driving is a different thing than charging to 100% and then letting it sit for a week. Or driving to turtle-mode and then letting it sit for a week.

So in short, 80-20 is a good rule of thumb. But don't let it stop you from using the car as you need to. Just try to minimize sitting at the extremes for long durations and do a full charge occasionally to help keep the cells balanced.
I noticed you're still working with polymers.

LeftieBiker
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Re: Battery Management Strategy

Tue Apr 24, 2018 11:58 am

Yeah, I'd like to get my hands on the morons who suggest, on some official-looking site, fully draining a lithium battery just to get a slightly more accurate SOC reading. There is NEVER a good reason to do that, as just going to 20% will get it accurate enough. Remember that the BMS in a Leaf will never show a real 100% or 1% anyway.
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Zugzwang
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Re: Battery Management Strategy

Wed Apr 25, 2018 6:03 am

Thanks a ton guys. That's a bunch of info to look at and digest. (Links appreciated!) It sounds like to keep thing simple, ultimately, I should just push for the 20-80 range and not overthink it to the point that it messes with what I want to actually use the car for.

goldbrick
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Re: Battery Management Strategy

Wed Apr 25, 2018 9:34 am

Zugzwang wrote:It sounds like to keep thing simple, ultimately, I should just push for the 20-80 range and not overthink it to the point that it messes with what I want to actually use the car for.


Yep. A big part of why I bought my Leaf was the low TCO - total cost of ownership - including 'everything'. If you spend time fretting about how to micro-manage the battery that's a cost. And an easy one to mitigate.

LeftieBiker
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Re: Battery Management Strategy

Wed Apr 25, 2018 12:40 pm

Zugzwang wrote:Thanks a ton guys. That's a bunch of info to look at and digest. (Links appreciated!) It sounds like to keep thing simple, ultimately, I should just push for the 20-80 range and not overthink it to the point that it messes with what I want to actually use the car for.


Yes, but don't worry too much about going to 100% or down to 10% or so, as long as you make sure that you either drive the car shortly after (100%) or recharge ASAP (10%).
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IssacZachary
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Re: Battery Management Strategy

Thu Apr 26, 2018 1:32 am

LeftieBiker wrote: Yes, but don't worry too much about going to 100% or down to 10% or so, as long as you make sure that you either drive the car shortly after (100%) or recharge ASAP (10%).

Good tip!

When you need the range you can set the charge timer to come on in the morning and charge to 100% right before you leave home. That way your battery doesn't sit at 100% for very long.

And if you get home with less than 20% you can charge it with the timer override button. Then when it's over 30% (one blue dot on permanently, the other flashing) you can unplug the car and plug it back in again so that it will wait until morning to finish charging up to 100%.

That is if you really need 100% and you have a level 2 charging cable.
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LeftieBiker
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Re: Battery Management Strategy

Thu Apr 26, 2018 2:35 am

And if you get home with less than 20% you can charge it with the timer override button. Then when it's over 30% (one blue dot on permanently, the other flashing) you can unplug the car and plug it back in again so that it will wait until morning to finish charging up to 100%.


This is also a good strategy for recharging in Hot weather. Get it up to 30% or so, preferably with L-1 if possible, then unplug and wait until early morning to charge again, to let the pack cool off.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

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