DonDakin
Posts: 376
Joined: Wed Aug 15, 2012 7:10 pm

Best charging practices for battery longevity

Tue Aug 28, 2012 8:43 pm

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....

oahumiev
Posts: 57
Joined: Thu Jan 26, 2012 12:32 am
Location: Oahu, Hawaii

Re: Best charging practices for battery longevity

Tue Aug 28, 2012 9:43 pm

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.

Don
Site Moderator
Posts: 2464
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Best charging practices for battery longevity

Wed Aug 29, 2012 7:08 am

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
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
1979 Honda CBX six into six

danpatgal
Posts: 202
Joined: Mon Feb 27, 2012 10:21 am
Location: Ephrata, PA

Re: Best charging practices for battery longevity

Wed Aug 29, 2012 9:00 am

Don wrote: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.

MLucas
Posts: 833
Joined: Thu Jun 07, 2012 8:52 am
Location: Niagara on the Lake, Ontario, Canada

Re: Best charging practices for battery longevity

Wed Aug 29, 2012 10:31 am

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).

Like Dylan...I went electric.

  • Purchased: June 29th, 2012
  • Mileage on June 29th, 2013 - 25,431 km / 15,802 miles
  • Mileage on June 29th, 2014 - 51,286 km / 32,616 miles

List of Oil Spills: http://en.wikipedia.org/wiki/List_of_oil_spills

archie_b
Site Moderator
Posts: 126
Joined: Sun Dec 25, 2011 5:51 pm

Re: Best charging practices for battery longevity

Mon Jun 17, 2013 9:12 am

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/arti ... _batteries

tomrh
Posts: 33
Joined: Tue Jun 18, 2013 12:27 pm
Location: Norway

Re: Best charging practices for battery longevity

Tue Jun 18, 2013 12:51 pm

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. :o Bearing that in mind, I always charge to 100% and drive all the way down to the turtle if necessary.
Black 2012 i-MiEV, 70k miles.
Black 2012 Leaf.

jray3
Posts: 1352
Joined: Tue Dec 06, 2011 1:05 am
Location: Tacoma area, WA
Contact: Website

Re: Best charging practices for battery longevity

Tue Jun 18, 2013 1:12 pm

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:
2012 i-SE "MR BEAN" 70,000 miles
i-ES traded at 21,648 miles
2000 Honda Odyssey
1987 F250 Diesel
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

Don
Site Moderator
Posts: 2464
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Best charging practices for battery longevity

Tue Jun 18, 2013 2:24 pm

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
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
1979 Honda CBX six into six

tomrh
Posts: 33
Joined: Tue Jun 18, 2013 12:27 pm
Location: Norway

Re: Best charging practices for battery longevity

Tue Jun 18, 2013 11:46 pm

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.).
Black 2012 i-MiEV, 70k miles.
Black 2012 Leaf.

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