alohart
Posts: 1569
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu Jan 10, 2019 11:50 am

tman66 wrote:Is there any particular reason why the battery should be at ~50% and not let’s say 100%?

A Li-ion battery cell degrades more rapidly as its charge level varies from ~50% (i.e., more rapidly at very low or very high charge levels compared with mid-range charge levels). The i3's battery management system doesn't allow its cells to reach 0% or 100% charge levels to protect them from rapid degradation. According to the excellent book Electric Vehicles and the BMW i3 (60 Ah and 94 Ah) by David J. Bricknell, a 60 Ah battery pack can't be discharged lower than ~10% (a displayed charge level of 0%) or charged higher than ~95% (a displayed charge level of 100%). So if a battery pack is allowed to remain at a displayed charge level of 100%, the actual 95% charge level is still quite high and results in cells degrading more rapidly than at lower charge levels.

Many of us who plan to keep our i3's past the battery pack warranty period do what we can to minimize the inevitable battery cell degradation rate. Minimizing the time a battery pack is allowed to remain at a high charge level is one of these strategies.

For those leasing an i3 or who don't plan to keep their i3's for many years might feel that manually managing the battery pack's charge level is more trouble than they want to endure, so they just leave their EVSE's plugged in to their i3's whenever they're parked at home.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

tman66
Posts: 51
Joined: Tue Oct 02, 2018 12:10 pm
Location: Guelph, ON, Canada

Re: BMW i3 auxiliary battery sizes

Thu Jan 10, 2019 2:01 pm

Thanks Jim and again Art for more info. Decisions to make for sure.
2014 i3 BEV | 2011 328xi Wagon

EVMan
Posts: 282
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: BMW i3 auxiliary battery sizes

Thu Jan 10, 2019 10:02 pm

BMW is running the Chargeforward program in some places in US, and it encourages to charge to 100% every time , and when ever possible.
Most people are the Lease , so they could also care less .



alohart wrote:
tman66 wrote:Is there any particular reason why the battery should be at ~50% and not let’s say 100%?

A Li-ion battery cell degrades more rapidly as its charge level varies from ~50% (i.e., more rapidly at very low or very high charge levels compared with mid-range charge levels). The i3's battery management system doesn't allow its cells to reach 0% or 100% charge levels to protect them from rapid degradation. According to the excellent book Electric Vehicles and the BMW i3 (60 Ah and 94 Ah) by David J. Bricknell, a 60 Ah battery pack can't be discharged lower than ~10% (a displayed charge level of 0%) or charged higher than ~95% (a displayed charge level of 100%). So if a battery pack is allowed to remain at a displayed charge level of 100%, the actual 95% charge level is still quite high and results in cells degrading more rapidly than at lower charge levels.

Many of us who plan to keep our i3's past the battery pack warranty period do what we can to minimize the inevitable battery cell degradation rate. Minimizing the time a battery pack is allowed to remain at a high charge level is one of these strategies.

For those leasing an i3 or who don't plan to keep their i3's for many years might feel that manually managing the battery pack's charge level is more trouble than they want to endure, so they just leave their EVSE's plugged in to their i3's whenever they're parked at home.
2017 33KWH Rex
Model 3 Long Range
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alohart
Posts: 1569
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu Jan 10, 2019 11:17 pm

EVMan wrote:BMW is running the Chargeforward program in some places in US, and it encourages to charge to 100% every time , and when ever possible.
Most people are the Lease , so they could also care less .

That's true. I fear that the i3 will get a poor reputation down the road as battery degradation reduces range to unusable levels for many people while the cost of battery pack replacement remains a significant portion of the total value of an i3.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

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