Best State of Charge for storing i-Miev?

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cometboy

Member
Joined
Nov 18, 2013
Messages
11
Location
Adelaide, South Australia
What SOC should we leave our i-Miev at when storing them for several months?

My assumption has always been that the 80% figure was the magic number when storing cells with this chemistry. I currently store the i-Miev and numerous unused LiPo’s at this value for 4 to 5 months each year. I also note that and my fancy LiPo charger (these LiPo’s are used with various multirotor copters I play with) takes the cells to 80% when using the inbuilt “Storage” feature of the charger.

Would be interest in the current view on this topic and my best option here.....

The Aux battery is stored connected to a small regulated solar trickle charger during storage periods.

Bruce
 
I believe Mitsu recommends 30% or less for long term storage

Edit - I did a search and found this: "Quote from the green 17 page owner’s handbook. Page 16 states “Make sure the battery’s energy level gauge shows 2-4 bars”. “Do not leave the battery charged with more than 4 bars”. “Check the battery residual every 3 months and if you see any discharge, please charge to 2-4 bars”.

Owners report little if any self discharge, even after 6 months or more. I have one of our iMiEV's stored in the garage for a year now sitting on 3 bars - SOC hasn't changed since I put her away. I have an AGM 12 volt battery in her and it doesn't self discharge very quickly either. I do top off the 12 volt with a trickle charge every few months though

Don
 
We already have a thread Why do Li-Ion Batteries Die?: http://myimiev.com/forum/viewtopic.php?f=23&t=2007
Can't remember if Jeff Dahn's Dalhousie University presentation addressed this issue - all I remember is that temperature is a cell killer. BTW, he's now involved with Tesla: http://fortune.com/2015/06/17/meet-teslas-new-weapon-a-battery-scientist/

Don't have access to all my references, but here are a few random datapoints:

When dakine shipped his i-MiEV to Rarotonga in a shipping container, if I recall he was told by Mitsu to keep the charge level around three bars.

30%-50%
Ref: http://www.mpoweruk.com/storage.htm
Ref: http://www.powerstream.com/Storage.htm

40%
Ref: https://zeusbatteryproducts.wordpre...an-of-lithium-ion-batteries-in-home-business/
Ref: http://batteryuniversity.com/learn/article/how_to_store_batteries
Ref: https://en.wikibooks.org/wiki/Battery_Power/Lithium_Ion_Batteries

Best to rely on more-recent authoritative technical publications.
 
Added confusion came from reading the ImieV Owner’s Manual for our Australian delivered models. This is photograph from our MY12 Jan2012 manual.

IMievBatStr.jpg


This is also the procedure that was used by the dealer when the vehicles were stored for a couple of years...

Yes, high temperatures in our summers (38-41C) is the biggest issue with the chemistry for sure.

Thanks for the excellent references and I will change my bad ways and use 40%!

BTW, I did check (questioning the manual) last year with the Mitsubishi head Office for Australia (located in my city) and have an email reply stating that same thing!! I also asked about the 200km brake fluid replacement schedule stated in the manual - wow!!

Maybe after 2012/13 they changed the information?

Interestingly a few years on the range is still over 100km easily. And about 85-90km running the AC on hot days

Bruce
 
Even today there is a lot of mis-information going around about batteries, but I won't get into that.

I wonder if the earlier i-MiEVs periodically engaged the HV system to top off the 12 volt battery like the LEAF and Tesla vehicles do and that is why Mitsubishi originally said to fully charge the battery? Or did they just not know what the proper storage technique was at the time (and way over-estimate self-discharge)?

I would follow the 3-4 bars advice, and keep the car somewhere where temperature stays near room temperature (70-75 F).
 
I suspect that there's probably an optimum storage SoC vs. Temperature relationship that we're not privy to. Without picking nits, my *guess* is that storing the i-MiEV just about anywhere in that lower SoC region and keeping the car cool will certainly be preferable to keeping it at 80%-100% SoC in a hot climate.

Came across this set of graphs of capacity loss over time at various temperatures for various chemistries that might be of general interest, but none addressing our i-MiEV's large-format Lithium chemistry:
http://data.energizer.com/PDFs/temperat.pdf

We're about to take off for an extended trip around the US in the Tesla and I'll simply leave the i-MiEV charge levels in the 3-6 bar range and stick float chargers on the 12v and not worry about it... :geek:
 
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