Always charge to 100%?

[Tacfoto]

I am fortunate that my office provides free charging, and has enough chargers that I can park and charge all day while I am at work. We have six chargers and I've never seen more than 4 in use on my shift (I work 2PM to 10PM. My commute is 12 miles so I usually don't charge at home.

So for best battery life in years, is it best that I let the car charge to 100%? I've read that for Lithium ION cells it's best to stay between 30 and 80% for the the best life. Here is a video where the guy says just that: https://youtu.be/TdUqQZC2dcE?t=6m56s

Many EVs let you set a max capacity, you can limit the car to 90 or 80%, but BMW does not as far as I can tell.

 

[jadnashuanh]

BMW 'fudges' both 100% and 0% on their battery management logic. In four years, I've not noticed an issue on my battery capacity and I just leave mine plugged in all the time when I'm home. Note, the logic disconnects the actual incoming power once the car determines the battery is charged, so it's unlike a typical cellphone, or even many of the other EVs out there. There's an eBook out there on the i3, and it has an interesting statement in it that ten charges from 90-100% put the same wear on the battery as one from 0-100%. The actual chemistry in a battery helps determine it's ultimate characteristics...some are better at it than others. IOW, not all LiOn batteries are created equal.

 

[viking79]

I have a similarly short commute and only charge a few days a week at work, typicallywhen it gets to half. Come winter I will leave it plugged in at work to condition battery with a departure time.

BEV I would keep plugged in so it was always ready, my REx I just use gas every now and then when I didn't have it charged all the way and drove more than I thought I would need to, as I need to burn through the gas every few months anyway.

 

[alohart]

So for best battery life in years, is it best that I let the car charge to 100%? I've read that for Lithium ION cells it's best to stay between 30 and 80% for the the best life.

I know of no reason why the Samsung SDI battery cells that BMW uses should be any different from any other Li-ion cell in this respect. It's an electrochemical fact that a cell at a high charge level is more reactive than at a lower charge level. This increased reactivity leads to the acceleration of destructive, non-reversible side reactions that degrade a cell.

By not allowing its cells to charge to 100%, BMW has reduced, but not eliminated this problem. BMW must have calculated that by limiting full charge to 92-95% of the actual full charge, this degradation will be slow enough that few battery packs would need to be replaced under warranty due to capacity degradation exceeding 30%.

Those who lease their i3's would not be affected significantly by such degradation. However, those of us who have purchased our i3's and plan to keep them past the expiration date of our battery packs might be significantly affected by capacity degradation unless we proactively manage our battery packs. I typically charge to an indicated 90% and then charge fully just prior to departing if I think I'll need full range. To accelerate the battery cell charge level balancing process, I try to charge fully monthly and then allow our i3 to remain at full charge at least overnight.

If my battery pack management results in a loss of usable capacity due to battery cell charge imbalance, this could be fixed by allowing the battery pack to remain at full charge for longer periods. This is preferable to losing usable capacity due to degradation that is permanent and cannot be fixed except by replacing battery cells.

 

[jadnashuanh]

The way I look at it is this: assuming the battery lasts at least the 8-years of the warranty, should I still want to keep the car, the battery tech will likely be significantly better and I can swap it out at that time. Plus, even a battery pack that isn't capable of full charge would still be useful to incorporate into an energy storage system for my home. Because more of the packs will become available as time goes by, the availability of that hardware needed to implement it will increase and the costs will likely go down as well.

Even at half capacity, it would likely be enough for a full day of use for my home, and more if I were needing to conserve because of a major grid problem. My heating system doesn't use much power (gas boiler), so keeping my refrigerator and maybe a few lights, it could last probably 4-5 days or more.

If you look at the progress since the i3 was originally released, the capacity in the same volume has increased significantly, with another increase predicted for next year. At some point, they may have to redesign the battery compartment and it may or may not still fit on the older vehicles. Time will tell. But, again, the i3 isn't like your typical cellphone battery. By varying the proportions of components, the cell size, and anode/cathode materials, you can vary how it reacts to charging and its longevity. Different tech, but maybe a similar idea, the NiCad batteries on my sister's Prius are over 10-years old, and it's still working. Those typically have a predicted life much shorter than LiOn ones. Not apples-apples, I know, but good design does affect the life of the things. BMW ran prototypes for years prior to releasing the i3. Major new EVs from them have been waiting for the next generation cells, but the i3 did make a statement. It has been selling lots more than they originally planned for. Mine is one of the first in the country (built April 2014). Still going strong.

 

[EVMan]

Can we get share some real numbers of battery degradation.
So this is my case. At 20K and 2 years , my battery has gone down to 17.9 KWH at perfect weather. and this seams to be accelerating trend now. I can see it going down now rapidly. So the battery degradation is little higher than the typical 6% stabilization data from the tesla forum.
So while i have only heard good things of the SDI battery , i believe the higher degradation is caused by charging the car to 100% or 96% every time..
Since the battery buffer is on both sides, the 93% battery used is like 3%-96% or charging to 96%.
If people know , tesla uses very simple small cylinder cells , but a lot of them. They achieve longer life , with better battery management. If you would charge a Tesla to 96% every time, i would guess, the degradation will be much higher 6%.

So for best battery life in years, is it best that I let the car charge to 100%? I've read that for Lithium ION cells it's best to stay between 30 and 80% for the the best life.

I know of no reason why the Samsung SDI battery cells that BMW uses should be any different from any other Li-ion cell in this respect. It's an electrochemical fact that a cell at a high charge level is more reactive than at a lower charge level. This increased reactivity leads to the acceleration of destructive, non-reversible side reactions that degrade a cell.

By not allowing its cells to charge to 100%, BMW has reduced, but not eliminated this problem. BMW must have calculated that by limiting full charge to 92-95% of the actual full charge, this degradation will be slow enough that few battery packs would need to be replaced under warranty due to capacity degradation exceeding 30%.

Those who lease their i3's would not be affected significantly by such degradation. However, those of us who have purchased our i3's and plan to keep them past the expiration date of our battery packs might be significantly affected by capacity degradation unless we proactively manage our battery packs. I typically charge to an indicated 90% and then charge fully just prior to departing if I think I'll need full range. To accelerate the battery cell charge level balancing process, I try to charge fully monthly and then allow our i3 to remain at full charge at least overnight.

If my battery pack management results in a loss of usable capacity due to battery cell charge imbalance, this could be fixed by allowing the battery pack to remain at full charge for longer periods. This is preferable to losing usable capacity due to degradation that is permanent and cannot be fixed except by replacing battery cells.

 

[i3Houston]

Wish there is central place where everyone can enter the Battery health.

Mine is 17.3% at 17K miles in 30 months, measured on 90F day. I charge my car every night to 100% since I bought it 4 months ago. .

Question - Is there a place to set the battery charge percentage? Thought only Teslas can do that

Can we get share some real numbers of battery degradation.
So this is my case. At 20K and 2 years , my battery has gone down to 17.9 KWH at perfect weather. and this seams to be accelerating trend now. I can see it going down now rapidly. So the battery degradation is little higher than the typical 6% stabilization data from the tesla forum.
So while i have only heard good things of the SDI battery , i believe the higher degradation is caused by charging the car to 100% or 96% every time..
Since the battery buffer is on both sides, the 93% battery used is like 3%-96% or charging to 96%.
If people know , tesla uses very simple small cylinder cells , but a lot of them. They achieve longer life , with better battery management. If you would charge a Tesla to 96% every time, i would guess, the degradation will be much higher 6%.

So for best battery life in years, is it best that I let the car charge to 100%? I've read that for Lithium ION cells it's best to stay between 30 and 80% for the the best life.

I know of no reason why the Samsung SDI battery cells that BMW uses should be any different from any other Li-ion cell in this respect. It's an electrochemical fact that a cell at a high charge level is more reactive than at a lower charge level. This increased reactivity leads to the acceleration of destructive, non-reversible side reactions that degrade a cell.

By not allowing its cells to charge to 100%, BMW has reduced, but not eliminated this problem. BMW must have calculated that by limiting full charge to 92-95% of the actual full charge, this degradation will be slow enough that few battery packs would need to be replaced under warranty due to capacity degradation exceeding 30%.

Those who lease their i3's would not be affected significantly by such degradation. However, those of us who have purchased our i3's and plan to keep them past the expiration date of our battery packs might be significantly affected by capacity degradation unless we proactively manage our battery packs. I typically charge to an indicated 90% and then charge fully just prior to departing if I think I'll need full range. To accelerate the battery cell charge level balancing process, I try to charge fully monthly and then allow our i3 to remain at full charge at least overnight.

If my battery pack management results in a loss of usable capacity due to battery cell charge imbalance, this could be fixed by allowing the battery pack to remain at full charge for longer periods. This is preferable to losing usable capacity due to degradation that is permanent and cannot be fixed except by replacing battery cells.

 

[alohart]

Can we get share some real numbers of battery degradation.

The problem is that i3 drivers have no easy way to get accurate battery capacity values. Batt. Kapa. max has varied by 4 kWh on our i3 with no up or down trend, so it cannot be used to determine degradation unless every measurement were made under exactly the same conditions which would be difficult.

Since the battery buffer is on both sides, the 93% battery used is like 3%-96% or charging to 96%.

David Bricknell's Electric Vehicles and the BMW i3 (60Ah and 94Ah) states that the usable capacity range is between 10% and 92-96%, depending on temperature, discharge/charge power, etc. That means that 82-86% of the total capacity is usable.

 

[alohart]

Mine is 17.3% at 17K miles in 30 months, measured on 90F day. I charge my car every night to 100% since I bought it 4 months ago. .

Are you stating that your battery pack has lost 17.3% of its capacity or that its current Batt. Kapa. max value is 17.3 kWh? If you feel that your battery pack has lost 17.3% of its capacity, how have you been able to determine this, especially to such precision?

As many have stated, Batt. Kapa. max isn't a particularly accurate measurement of capacity unless repeated measurements are made over many months at exactly the same conditions which is almost impossible to do.

Question - Is there a place to set the battery charge percentage?

Unfortunately not. Using the charging power of our EVSE, I know that manually stopping charging 1 hour before the estimated charging end time displayed on the instrument panel results in a final displayed charge level of ~90%. Our JuiceBox EVSE supports timed charging or I can set an alarm on my watch to remind me to manually quit charging.

 

[i3Houston]

Sorry... current Batt. Kapa. max value is 17.3 kWh