BMW i3 – batteries and charging solutions

As part of the upcoming BMWi Innovation Days, BMW has released more details on the i3 electric vehicle, its battery technology and charging solutions.

Lots of info.

http://www.bmwblog.com/2013/04/18/bmw-i3-batteries-and-charging-solutions/

Here is the English version with some different photos.


http://www.bimmerfest.com/forums/showthread.php?p=7530269

One thing that did surprise (& shock) me a bit was this ........."After around 1,000 charging cycles, the battery retains most of its rated capacity" surely that’s less than 3 years of a charge a day - that doesn't sound like "Battery lasts the life of a vehicle" as described elsewhere.

Parker said:

Here is the English version with some different photos.


http://www.bimmerfest.com/forums/showthread.php?p=7530269

One thing that did surprise (& shock) me a bit was this ........."After around 1,000 charging cycles, the battery retains most of its rated capacity" surely that’s less than 3 years of a charge a day - that doesn't sound like "Battery lasts the life of a vehicle" as described elsewhere.

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Parker, I know you are very interested in the i3 so I am a bit surprised by this comment. Please take some time to research EV battery basics when you get a chance, I don't want you to by the i3 or another plug in car and then be disappointed. Here's the facts on battery life:

The battery begins to degrade immediately once you buy the car. After some use it is never as good as it was when it was new. You may not be able to immediately measure the degradation because it is small, but you would be able to is you had the ability to measure it's capacity. I have just passed my 1,000th recharge on my BMW ActiveE and have 8% capacity loss meaning I can only drive it 92% as far as I could a mere 15 months ago. This is normal. The ActiveE has the same batteries the i3 will use so I feel fairly certain the results will be very similar when I get my i3. I do drive a LOT and have 45,000 miles on the car in only 15 months with 1,000 recharges. This would represent about 2.5 to 3 years for the average person. If the i3 battery only degrades 8-10% in three years of normal use that I will rejoice because that is VERY good. Most other EV batteries lose more capacity over that time period. The LEAF has a huge problem with this particularly in hot weather areas and some owners have experiences nearly 30% capacity loss after only two years of use. However the LEAF doesn't have a complex thermal management system which by keeping the batteries at the proper temperature will ward off early degradation and capacity loss.

I recently did a story for plugincars.com on the importance of manufacturers and dealers to explain this to customers before they buy an EV. here is the link:
http://www.plugincars.com/electric-car-dealers-must-address-concerns-about-batteries-126992.html

I am also working on a more detailed story of my personal experience with degradation for BMWBLOG and that will be up on that site within a week. Please take some time to understand how degradation will effect your cars range over the lifetime so you are not surprised when you get one. You will not be able to drive an EV the same distance you could when it was new after a couple years of ownership and eventually (8-12 years depending on use) you will have to replace the battery and that will be a big expense.

Tom many thanks for the comprehensive reply and link.

I appreciate I’m at the beginning of my EV learning journey – that’s why these forums are so great – I’m a bit like a surfer riding the crest of EV info on the run up to the launch of the i3. That’s probably why I found this bit of PR /Infotainment on the i3 batteries so confusing.
On the one hand BMW were saying their batteries were designed to last the life of the car (and to my un-engineering brain a car made out of aluminium and Carbon Fibre would last a pretty long time – certainly longer than 10 years – and in my mind I was thinking 20+ years maybe) yet on the other hand the article was saying 1,000 re-charges would be an acceptable life span for a battery (maybe 3 years) – to someone like me with no life experience of an EV such a confused message just adds another layer of doubt – i.e. If BMW don’t know how long their batteries will last (a window of 3-20 years isn’t a window .....its just guessing!) – how am I supposed to budget for replacements – a hapless consumer.

Parker said:

Tom many thanks for the comprehensive reply and link.

I appreciate I’m at the beginning of my EV learning journey – that’s why these forums are so great – I’m a bit like a surfer riding the crest of EV info on the run up to the launch of the i3. That’s probably why I found this bit of PR /Infotainment on the i3 batteries so confusing.
On the one hand BMW were saying their batteries were designed to last the life of the car (and to my un-engineering brain a car made out of aluminium and Carbon Fibre would last a pretty long time – certainly longer than 10 years – and in my mind I was thinking 20+ years maybe) yet on the other hand the article was saying 1,000 re-charges would be an acceptable life span for a battery (maybe 3 years) – to someone like me with no life experience of an EV such a confused message just adds another layer of doubt – i.e. If BMW don’t know how long their batteries will last (a window of 3-20 years isn’t a window .....its just guessing!) – how am I supposed to budget for replacements – a hapless consumer.

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Parker: How long the battery "lasts" is really up to you. By that I mean how much degradation are you willing to live with. It's generally accepted in the EV industry that once an EVs battery has degraded to 80% of its original capacity then it has reached its end of life and needs to be replaced. The battery still works fine, and will then be repurposed for a 'second life' use as an energy storage device. However that doesn't mean you HAVE to replace it if it still gives you the range you need. Lets say you have an i3 and brand new it goes 95 miles per charge in moderate conditions. Then, after 5 years and 80,000 lets assume the battery can only propel the car 75 miles under the same conditions. Is 75 miles enough for you? By then public charging infrastructure will be much better than it is now and you may be able to opportunity charge during the day very easily making the lower range not much a problem. Plus, there may be quick charge stations in convenient locations to allow you to recharge to 80% in 25 minutes. So the level of acceptable degradation will vary from person to person. Some people may keep their original battery for 15 years if they manage it properly and don't drive too much. As you can see there are a lot of factors that will determine how long you use your original battery.

really have to pump this topic.

when the i3 got 22,600watthours.
and 18.800 is usable that 87% right?
so there is a window of just 13% not used for life durability

what i read from other ev's they normally dont discharge below 20% and never above 90%
so they reserve 30%... not 13%
so how are they expecting the i3 battery will last the 8 years or more?

GI3L said:

when the i3 got 22,600watthours.
and 18.800 is usable that 87% right?
so there is a window of just 13% not used for life durability

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Correct! The battery management system of the 94 Ah battery pack makes 18% unusable, so for some reason, BMW increased this buffer.

GI3L said:

what i read from other ev's they normally dont discharge below 20% and never above 90%
so they reserve 30%... not 13%

Click to expand...

That sounds high, but I've not found any source that compares the reserved buffer percentages for every EV. The original Nissan Leaf has a 24 kWh battery pack, 21.3 kWh of which is usable. That's an unusable percentage of only 11%, less than the 60 Ah i3.

GI3L said:

so how are they expecting the i3 battery will last the 8 years or more?

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We don't know BMW's calculation. They probably figured that by the time an i3's battery pack fails under warranty, replacement battery packs would be considerably less expensive, so replacement costs wouldn't be nearly as high as when the car was new. They might do as Honda did with its early hybrids and use rebuilt battery packs as warranty replacement packs. BMW could use "good" modules from wrecked i3's or from failed battery packs to build warranty replacement battery packs (not all modules in a failed back are "bad").

Like other early EV manufacturers, to get acceptable range, BMW had to push the limit of the i3's battery pack due to its high cost/kWh, high weight/kWh, and high volume/kWh, so BMW reduced the unusable buffer as much as possible, even if doing so might shorten the battery pack's usable life. Maybe with the improved volume and charge densities of the 94 Ah battery pack, BMW could afford to increase the unusable buffer to extend the battery pack's usable life without decreasing the range to an unacceptable level.

The tiny 3% high charge unusable buffer that the 60 Ah battery management system uses (i.e., the battery pack can be charged to 97% of its actual maximum charge) might lead to faster degradation if one fully charges every night and allows the battery pack to remain at full charge for hours before driving. So I fully charge only if I think that I might need the full range the following day, and I delay the start of charging so that the battery pack won't remain at the fully-charged state for very long.

alohart said:

GI3L said:

when the i3 got 22,600watthours.
and 18.800 is usable that 87% right?
so there is a window of just 13% not used for life durability

Click to expand...

Correct! The battery management system of the 94 Ah battery pack makes 18% unusable, so for some reason, BMW increased this buffer.

GI3L said:

what i read from other ev's they normally dont discharge below 20% and never above 90%
so they reserve 30%... not 13%

Click to expand...

That sounds high, but I've not found any source that compares the reserved buffer percentages for every EV. The original Nissan Leaf has a 24 kWh battery pack, 21.3 kWh of which is usable. That's an unusable percentage of only 11%, less than the 60 Ah i3.

GI3L said:

so how are they expecting the i3 battery will last the 8 years or more?

Click to expand...

We don't know BMW's calculation. They probably figured that by the time an i3's battery pack fails under warranty, replacement battery packs would be considerably less expensive, so replacement costs wouldn't be nearly as high as when the car was new. They might do as Honda did with its early hybrids and use rebuilt battery packs as warranty replacement packs. BMW could use "good" modules from wrecked i3's or from failed battery packs to build warranty replacement battery packs (not all modules in a failed back are "bad").

Like other early EV manufacturers, to get acceptable range, BMW had to push the limit of the i3's battery pack due to its high cost/kWh, high weight/kWh, and high volume/kWh, so BMW reduced the unusable buffer as much as possible, even if doing so might shorten the battery pack's usable life. Maybe with the improved volume and charge densities of the 94 Ah battery pack, BMW could afford to increase the unusable buffer to extend the battery pack's usable life without decreasing the range to an unacceptable level.

The tiny 3% high charge unusable buffer that the 60 Ah battery management system uses (i.e., the battery pack can be charged to 97% of its actual maximum charge) might lead to faster degradation if one fully charges every night and allows the battery pack to remain at full charge for hours before driving. So I fully charge only if I think that I might need the full range the following day, and I delay the start of charging so that the battery pack won't remain at the fully-charged state for very long.

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thx for your reply.

so it charges to 97% and then not lower then 10%...

the battery pack is about 50% bigger then the volts battery pack ( 16kwh firs model year ) so the amount of enegry at 20% of the volt battery pack would be the same as 15% with the i3 right?

so its only 5% lower then the volt in energy amount.

the car is lighter so its also easyer on the battery cells ( if you dont step on it )

and yes if you charge it to 97% and drive off direct after it would not be that mouch of a problem

cant you set a departure time and have it ready just before that? so you always have 97% and drive of directly after?

how long do you have your i3 now and did you see any degradation? ( you know that menu where you can look that up right? )

GI3L said:

so it charges to 97% and then not lower then 10%...

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According to Electric Vehicles and the BMW i3 (60Ah and 94Ah).

GI3L said:

the battery pack is about 50% bigger then the volts battery pack ( 16kwh firs model year ) so the amount of enegry at 20% of the volt battery pack would be the same as 15% with the i3 right?

so its only 5% lower then the volt in energy amount.

Click to expand...

Wikipedia claims that only 10.3 kWh of the 16 kWh first generation Volt battery pack is usable, so its 36% unusable buffer is much larger than the i3's. That would mean that the 60 Ah i3's battery pack has 83% more usable energy.

GI3L said:

cant you set a departure time and have it ready just before that? so you always have 97% and drive of directly after?

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The i3's charging settings have been buggy and seem unnecessarily complex. I think the bugginess has improved in recent software versions, but I never use these settings because our EVSE can be set to start and end charging reliably at specific times.

I believe the only way to delay the charging start time using the i3's settings is to set a low-cost charging time period and a departure time. I think the i3 will then start charging early enough to ensure that the battery pack would be fully charged before the departure time. If a full charge would occur by starting the charge at the start of the low-cost charging time period, then that time is used.

Someone familiar with the i3's charging settings could comment on how much in advance of the departure time a full charge would be reached.

GI3L said:

how long do you have your i3 now and did you see any degradation? ( you know that menu where you can look that up right? )

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We bought our i3 BEV new in November, 2014, but have driven it only 3.9k miles (6.2k km), so I would not expect any noticeable battery pack degradation. The batt. kapa. max values have been scattered over almost 3 kWh with no trend obvious, but that might be because I don't read them in exactly the same circumstances each time. For example, 2 days ago, batt. kapa. max was 16.5 kWh, but yesterday it was 18.7 kWh. I have seen it over 19 kWh. So I don't know how to use batt. kapa. max to determine battery degradation.

A couple of other early i3 owners have driven over 50k miles (80k km) with no noticeable decrease in actual range. One of them, Tom Moloughney, has regularly recorded batt. kapa. max values under controlled conditions and has measured very little capacity decrease.

sorry thats only for apple users
cannot read that book

GI3L said:

sorry thats only for apple users
cannot read that book

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The book is readable here. Not sure if one can download a copy.