Best charging practices for battery longevity

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DonDakin

Well-known member
Joined
Aug 15, 2012
Messages
387
Location
Montreal Quebec.....
Hi all,

I thought it might be an interesting topic to discuss charging practices.

I have read the the Leaf has an option to do an 80% charge. I believe this is to have the battery last longer. So I wonder if that is a good practice for the iMiev battery.

I think the owners manual says to discharge down to 2 bars or less and then fully charge to calibrate the fuel gauge every few months. That's the only thing that I saw regarding charging other then the cold/hot weather and quick charging warning. Nothing in the manual saying this is the optimal way to charge and keep the Battery in good shape.

Considering the leaf 80% option it correct to assume that charging only 50% would even further increase battery life ? (I think the volt is doing something like this)

Anyone with some Lithium ion battery knowledge out there ?

I'm thinking that if I could get along with Level 1 charging at 120V/8 amps and charged from 2 bars to 12 bars (out of 16 total) that would give me about 65 km (40 Miles) of range per day which is fine for me and I think fine for the battery, slow charging and only using 75 % of capacity and keeping the battery well above fully depleted.

Any opinions ?

Don....
 
Don, this has been discussed in other threads previously with some choosing to fully charge regularly while others pamper their batteries by not fully charging whenever possible and not dropping below 2 bars. We're still trying to figure out exactly what percentage of 16kwh battery our Miev uses. In general, keeping batteries at 50% SOC is best and out of extreme heat or cold. Also, using only slight charge/discharge cycles would be optimal but reduce the utility of our Miev.

It is true that to properly recalibrate our battery packs, we should take it down to 2 bars and fully charge although I believe that is more for the RR value to accurately reflect battery capacity remaining as opposed to a method of increasing the longevity of our batteries, someone can correct me if I'm wrong.
 
As a general rule, for most types of lithiums in general, the general conscensus seems to be . . . . keep the SOC between 30% and 80% as much as possible :lol:

I have no idea how much extra life you'd gain by following that advice, but it pretty much cannot hurt anything, so lately we've taken to 'time charging' so that the charge ends at about 13 or 14 bars as often as practical, which for us is most of the time. Since we almost never need the extra few miles of range from a fully charged pack, this doesn't affect the practicality of the car much for us . . . . so, why not? After the rare occasion that we do pull the battery down to 2 bars or less, we usually let it cool off for an hour or so and then recharge it fully - This is probably once a month or less

Get back with me in 7 or 8 years and I'll let you know how this is working out ;)

All that said, I'm fairly certain that Mitsu built in some pretty conservative charging algorithms into the car - How else could they warrant the battery for 8 years or 100K when they know most cars are not going to be used by 'techies' who pay particuar attention to the way they treat the battery pack?

Don
 
Don said:
All that said, I'm fairly certain that Mitsu built in some pretty conservative charging algorithms into the car - How else could they warrant the battery for 8 years or 100K when they know most cars are not going to be used by 'techies' who pay particuar attention to the way they treat the battery pack?Don
My feeling is there is effort, time, planning, and loss of use involved in babying the batteries that may or may not be worth it. I don't know, but I would guess that in 8 years (or 5-6) the battery technology will be better or cheaper, or both, so that getting a new set at that time won't be so painful and might result in improved range at that time.
 
The 80/20 rule doesn't work for me, although it sounds like a good rule if you can do it. My commute stretches the limits of the i's range and I like getting home with at least 4 bars left on the Power Meter. I've read draining the battery to Turtle Mode is even worse for the battery. I've only done that twice and never got to Red Battery Lite Mode (basically dead).
 
It's almost a year since the last post of this topic and I was wondering what experiences everyone has had over the last 10 months.

My comments pertain to the Volt but should apply to the Miev as well. I think we will all agree that cold weather is not very friendly to EVs and very cold weather is even worse. My observations apply to the eight or so months per year temperatures are more moderate and battery performance is more consistent.

I charge at night (off peak) using either a 120V 8/12 amp charger or a 240V 16amp charger. 95% of the time I notice no difference in range between the two chargers. Occasionally if using the 240V charger and I discontinue charging before a full charge, I observe a noticeable drop in miles per kwh. I normally get about 5 miles per kwh, but on these occasions it drops to around 4.2 miles per kwh. Driving exactly the same is impossible but my route does not vary much and neither do my speeds.

I charge once per day, everyday, except on weekends (off peak) where I may charge two or three times to give increased range. I rely of the car to determine when is the appropriate time to end charging. The only except to this is when I will not be using the car for a week or more. In those instances I leave the car charged at about 50% charge.

Here is a link to one of the better sites for battery and charging information:

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
 
There is a battery test from GS Yuasa, the manufacturer of the i-MiEV battery. Slide 8 tells us that after 1500 cycles at 25 degrees C, 81% capacity was reached. But then each cycle was a charge to 4.1V and a discharge to 2.75V. But the i-MiEV takes the battery only to 3.955 volts. And 2.75 volts is a much deeper discharge than the turtle. If we use table 4 in this article from batteryuniversity.com, then each 0.1 volt decrease would double the cycles. I.e. a value of 4.0 volts would double them, and 3.9 volts would quadruple them. So 3.955 volts gives us somewhat between, let's say three times. We then get approx 4500 cycles. Driving 60 miles a cycle, we get a breathtaking 270.000 miles before 81% capacity is reached. :eek: Bearing that in mind, I always charge to 100% and drive all the way down to the turtle if necessary.
 
Tusen Takk, Tomrh!

This bit of succinct analysis both gives me confidence of a long battery service life, and increases the desire to find the hack for a 4.1 V per cell "110% charge button" for those long-distance trips... :mrgreen:
 
Based on this report, If you get the hack figured out, I think I'll adjust mine to 3.855 :mrgreen:

I really wish we had an 80% or a 90% charge option - I'd use that every recharge. As it is, I try to do it manually most of the time and as a result, I occasionally fully charge it when I didn't intend to

Don
 
I think limiting the top level charge of i-MiEV was a good move from Mitsubishi. Users accept a "full" charge if displayed so - even if it is taken only to 80-90% behind the scenes. Nissan has chosen 4,11V as a default (slightly different battery chemistry however), but people are adviced to charge to 80%. Being limited to 80% feels rather - eh - limiting, and many owners charge to 100% anyway. Nissan is sweating considerably more over their battery warranty.

A hack for a range boost is definitively wanted. :D We drive the car so much that our warranty is probably voided in a year and a half anyway, and based on the GS Yuasa report the risk appears to be low. Probably a minor software update of the BMS. :mrgreen:

Btw - while cold weather is not very friendly for range, archie_b, it is quite friendly for battery longevity (cf. slide 8 of the GS Yuasa report, the 45 C curve.).
 
Tomrh:

I agree that cool temperatures are better for battery longevity, but slide 8 is showing the difference between 45C and 25C. This is 113F versus 77F, or very hot versus hot. Driving an EV, no matter what chemistry, at -10C to -20C (14F to -4F) or lower, does affect longevity. Just not to the degree that high temperatures (45C) do. Neither extreme is good for battery life.

Best would be 40F to 80F, like Seattle, WA. Rarely too cold and rarely too hot. Problem there is it rains, mists, is overcast, or foggy most of the time. Always green, but rarely sunny. Still, I enjoyed living there for 3 years.
 
MyNissanLeaf.com has an article about this. As far as I can understand, cold weather is optimal for battery life, and Rygge in Norway comes out with a very long battery life (~16,7 years estimated here for Leaf battery), only beaten by Juneau, Alaska, which is even colder! (cf. a table with cities further down in the article). I agree however that extremes are not good, there is a risk for lithium plating at a high SOC and very low temperatures. I assume that's why the cold weather package includes a battery heater.
 
archie_b said:
...Neither extreme is good for battery life.

Many articles out on net about this, all say that low temps leave no permanent damage to lithium-ion batteries unlike extreme heat (e.g. SouthWest Leafs). While my batteries did not endure extreme cold as say in Montreal (-25c), my batteries did get down to -15c and I don't see any loss in range this summer. I'm doing the same commute I did last year and I usually make it to Buffalo on 5-6 bars just like I did last year.
 
Here is a NASA report on the lithium plating effect: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41485/1/08-0012.pdf

Slide 4 shows a typical lithium cell charged at -40C (-40F), and the plating effect is obvious. Plating is an effect where the battery cannot receive all of the charge current, and lithium ions are deposited as solid lithium causing short-circuits leaving permanent damage to the battery. While several different battery chemistries show this effect already at -20C (-4F), the most commonly used today show no such effect, like e.g. the lithium manganese oxide at slide 22, that is "our" chemistry. :) Thus our batteries are safe down to at least -4F with normal charging. Below that temperature the i-MiEV shuts off the charger. The battery is still ok, but you cannot charge it. Nothing to worry about. The battery heater is there (if equipped) only to heat up the battery such that it can begin receiving charge again. Fast charging increases the risk for plating at low temperatures since the current is much higher, thats why fast chargers significantly reduce power when temperatures are low.
 
tomrh, thank you very much for sharing these links with us and adding to our body of knowledge about batteries. In my case, I'm happy that my iMiEV rarely even gets down to 32degF (0degC) and extreme high temperatures are rare since I live in a coastal area.
 
No problem, I'm just happy to be of any help. :) I have been active in a norwegian EV forum, but I have occationally been reading this forum as well because there's a lot of helpful advice to be found here! But a few days ago I noticed a post in this old thread about battery life worries. So I decided to register to share my thoughts. No need to worry when there's no reason to. In Norway, battery life worries is one of the main reasons why people won't buy an EV. It didn't exactly help that previous EV generations (lead-acid, NiCd, NiMH etc.) suffered from severe battery trouble every now and then, and had escalating expenses.
 
Being a new EV owner, I've never really had to worry about battery longevity before. However, I've had plenty of hobbies where a hardcore niche of hobbyists get really OCD about trying to eek every last bit out of whatever it is they do in their hobby. Is there truly a real concern about battery longevity in EVs? Or is all this talk another case of a core group of uber-geeks trying to push the envelope as far as possible? (**I hope I'm not offending anyone by using the term geek. I'm considered among the geekiest by friends and family.) Is using optimal charging strategies really going to have THAT big of an impact on the longevity and usefulness of my MiEV's batteries? Or is it only going to provide a minimum of improvement that is championed by us geeks but would never be noticed, recognized, and/or appreciated by the vast majority of the population?

My concern is that I don't want to give myself an anxiety attack worrying over whether I'm charging my car, not simply properly, but to its maximum efficiency. Normally, I would love to take a lot of time studying my charging habits and the effects thereof. But truthfully, I don't really have time for all that right now. My life has gotten really busy this past year since my second daughter arrived and my wife went back to work. These days it is more important that I actually make it to and from childcare, dropping my wife off at the train, and work each day than trying to maximize the optimal charge level in my EV. I don't want to have to worry every morning if there is enough charge to get me there and back based on my charging strategy. It would be most convenient to simply plug my i into the L2 charger every night and know that I will wake up in the morning with a full "tank" that will take me everywhere I need to go and then some.

With all that being said, if charging strategy truly has a significant impact on battery life and capacity, I'd prefer to make a little bit of time in my busy day to address my charging habits and avoid any premature and costly battery replacement expenses.
 
Robb - I think the jury is still out. There are users who are fully recharging everyday and some who fully recharge more often than once per day. There are also some who make regular use of the ChaDeMo Quick Charge process . . . . and then there are some of us who only fully recharge the pack once every 2 or 3 weeks. I suspect after some period of time, we'll begin to see how the battery pack fares depending on how it's been treated. Hopefully, nobody will begin to see any adverse effects for several years

But, it's certainly a fact that the overall economy of driving this car is a factor of what a new pack will cost when the time comes to replace it and how many miles you got out of the pack. If you really can drive it for 100,000 miles and the new pack costs $10,000, then your average mileage expense just went up by ten cents a mile . . . . plus whatever you paid for electricity. Consider that a 40 mpg ICE burning $3.50 a gallon gas is using less than 9 cents of fuel per mile

If you need it fully charged to make the trip you're headed out on, by all means, fully charge it but if you can get where you need to go on only 10 bars of juice, then leaving home with 12 or 13 showing is probably better for the battery - It SHOULD last longer doing this

I just wish Mitsu had given us the 80% charge option like Nissan did for the Leaf - I would use that nearly every time. It would be much less time consuming than manually stopping the charge process at about 80% which is what I do now

Don
 
Don said:
I just wish Mitsu had given us the 80% charge option like Nissan did for the Leaf - I would use that nearly every time. It would be much less time consuming than manually stopping the charge process at about 80% which is what I do now.

Yep, this is the part I'd like to figure out; only charging up to about 80% give or take. I would prefer to take measures that will extend the life of the battery pack and give me the biggest bang for my buck, but it would be nice if the process could be automated. Being a new i owner, I have NO idea how long to charge given a current SOC in order to reach that just-under-full charge. As has been mentioned in many other threads, I'm sure I will learn my car's charging needs as time goes on.

I used the remote timer for the first time last night to take advantage of lower rates in the wee hours of the night. Let me tell you, THAT was a confusing fiasco! It was VERY difficult to determine if the car was currently charging or properly set on a timed setting. The "Charging" light on the L2 EVSE kept going on and off, and I frequently got lots of beeping and errors on the remote. Anyway, I set the beginning time a certain number of hours from the current time (9pm) that would certainly be within the lower rate period. However, I did not set the end timer because I have no idea how many hours to go to reach a SOC that will get me everywhere I need to go throughout the day, but less than a full charge. I'm still too timid to risk not having enough charge when I leave in the morning. So, I let it continue to a full charge.

Speaking of the remote timer, that thing is confusing as heck and has a rather steep learning curve for such a "simple" device. The need to set the charging to manual using the remote before you can set the timer is annoying. Even more annoying is having to press the "comm link" between each command. But most annoying of all is the actual setting of the charging time! Why did MM make it based on hours from current time for a certain number of hours? This would have been MUCH simpler to use if I could just set it to start charging at 1am every night and stop charging at 6am. That way I could be certain it is charging at exactly the same time each night. A truly plug-and-play process. As it is now, I will either need to manually reset the remote timer every night based on the current time or wait until the same specific time every night before I plug in the i and start the remote timer.

I have another question about the remote timer. I know the remote retains the timer settings from the previous session so that you don't have to re-set it up every night. What I want to know is if those charging settings are stored in the i's memory somehow? For example, if at 9pm last night I had plugged in my i and set the remote to start charging in 4 hours and stop charging after 5 hours, will the i remember those settings? So, tonight would I be able to go out to the garage and simply plug the i in at 9pm and it will automatically adhere to the previous remote settings without me taking any other steps? Or do I have to go out at 9pm, plug the i in, transmit a manual charging signal to the i using the remote to stop the auto charging that started when I plugged in, and THEN go through the remote charging steps on the remote?
 
RobbW said:
I used the remote timer for the first time last night to take advantage of lower rates in the wee hours of the night. Let me tell you, THAT was a confusing fiasco! It was VERY difficult to determine if the car was currently charging or properly set on a timed setting. The "Charging" light on the L2 EVSE kept going on and off, and I frequently got lots of beeping and errors on the remote. Anyway, I set the beginning time a certain number of hours from the current time (9pm) that would certainly be within the lower rate period. However, I did not set the end timer because I have no idea how many hours to go to reach a SOC that will get me everywhere I need to go throughout the day, but less than a full charge. I'm still too timid to risk not having enough charge when I leave in the morning. So, I let it continue to a full charge.

What about using a light timer? You can buy one at a local hardware store for $5. They have some rated for 15 amps so good enough at the 110 charging level. Easy to set start and stop time mechanically.
 
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