[scottg61376]

All, avid BMW brand loyalist here. I’m contemplating purchasing a first year run low mileage i8 to keep as a long term collector. Wanted to check in to see if anyone had any info on potential challenges with driving less than 500 miles a year with the battery technology. Long ago I was advised to never buy a hybrid vehicle that you don’t actually plan on driving as the batteries get unhappy if left sitting for long periods of time.

Vehicle will be garage kept.

[FrequentFlyer]

I was looking into this as I was increasingly unable to drive mine (garaged) before biting the bullet and selling it. I did 1000 miles in a year going up to 3 weeks at a time without driving it.

The high voltage battery loses capacity faster with more charge in it so ideally you could leave it half charged if it is not used for a while. The i3 forums are the place to learn about the BMW Battery Technology as used the i8 so browse away over there for more detail....

Anyway the above guidance means not leaving it plugged in. If I left mine for a week without charge then it moved off on electric power but leave it more than 2 weeks then the ICE fired up on start. According to the app I found that the HV Battery lost about 1% of charge a week when it was not used so we are not talking about something that you need to watch like a Hawk.

You still have to drive it/charge it enough to keep the conventional LV battery healthy. You can do this with a drive every 2/3 weeks, fully charging the night before you take it out.

Good luck with your purchase.

[evanevery]

Originally Posted by scottg61376

All, avid BMW brand loyalist here. I’m contemplating purchasing a first year run low mileage i8 to keep as a long term collector. Wanted to check in to see if anyone had any info on potential challenges with driving less than 500 miles a year with the battery technology. Long ago I was advised to never buy a hybrid vehicle that you don’t actually plan on driving as the batteries get unhappy if left sitting for long periods of time.

Vehicle will be garage kept.

Just give it me me when you're not using it and I'll see that it gets some regular exercise. ;-)

[scottg61376]

Originally Posted by evanevery

Just give it me me when you're not using it and I'll see that it gets some regular exercise. ;-)

Ha, goal is to keep it under 5k miles, so that won’t work

[jcpca356]

brave soul. Had mine for about 4 years. just hit 10k miles. had the battery tested and it's perfectly healthy i store it in winters where i hardly drive it for months at a time

[wanesso]

I store mine all winter (real winter in the NE) with no charge, unheated garage for the last 3 winters and no problem first time or anytime I take it out in the spring. But I WILL be putting miles on it, way too fun to drive to watch it sit! With many produced, you really think it will be collectible?

[JasH]

Originally Posted by FrequentFlyer

The i3 forums are the place to learn about the BMW Battery Technology as used the i8 so browse away over there for more detail....

No, i3 has very different battery technology. (I own both cars.)

[JasH]

Originally Posted by wanesso

With many produced, you really think it will be collectible?

Probably yes it will. But in 15+ years.

[evanevery]

Not for nuthin', but....

Tesla recommends always keeping their cars plugged in if possible.

[FrequentFlyer]

Originally Posted by JasH

No, i3 has very different battery technology. (I own both cars.)

JasH, full respect for your knowledge of both cars. The point I wanted to make was that they both use NCM/NMC cells from Samsung SDI and have the same Battery Management Hardware, Software and Algorithms.

The lifecycle and degradation is going to behave in the same way (albeit that the i3’s Thermal Management System will be working harder to compensate for the higher charge and discharge rates of the pack). IIRC the Samsung Cell is good for about 4000 charge cycles at 25 degC before it drops to 80% capacity which they define as EOL. As the cell temperature climbs the charge cycles to EOL drops. The 8 year battery warranty looks a safe bet by BMW due to the Thermal Management System.

I didn’t find a definitive document on degradation curves at 100% SOC vs 50% but it seems widely accepted that rate of degradation increases with SOC for this Lithium chemistry.

[Edited to add degradation curves for 10 months storage, but bear in mind that BMW restricts the usable capacity of the i8 battery in the interests of longevity so you are never at 100% or 0% SOC. Chart b is the relevant one.

The lower charts show the progression of internal resistance which is responsible for the heating of the cells during charge/discharge. Again the trend is the same that storage at high SOC/high temp degrades the battery faster.

These charts are NOT for the specific cells that BMW use but show how the chemistry type behaves. Naturally degradation cannot be reversed and the effects are cumulative ]



If you are only keeping the car for a couple of years then this is totally irrelevant but anyone looking at a 15 year classic car horizon might be interested.

The attached BMW presentation is a great top level summary of the i3 and i8 batteries.

high_voltage_batteries_of_bmw_vehicles.pdf

[JasH]

There is a significant difference between both battery types.


i3 is designed for slower discharge. i8 battery is designed for rapid charge and discharge, but with a lower output, more similar to a KERS battery.

I was told this by one of the i8 designers personally. It also makes sense, given the usage profile of the battery in each car.

[Groundhog]

Originally Posted by FrequentFlyer

JasH, full respect for your knowledge of both cars. The point I wanted to make was that they both use NCM/NMC cells from Samsung SDI and have the same Battery Management Hardware, Software and Algorithms.

The lifecycle and degradation is going to behave in the same way (albeit that the i3’s Thermal Management System will be working harder to compensate for the higher charge and discharge rates of the pack). IIRC the Samsung Cell is good for about 4000 charge cycles at 25 degC before it drops to 80% capacity which they define as EOL. As the cell temperature climbs the charge cycles to EOL drops. The 8 year battery warranty looks a safe bet by BMW due to the Thermal Management System.

I didn’t find a definitive document on degradation curves at 100% SOC vs 50% but it seems widely accepted that rate of degradation increases with SOC for this Lithium chemistry.

If you are only keeping the car for a couple of years then this is totally irrelevant but anyone looking at a 15 year classic car horizon might be interested.

The attached BMW presentation is a great top level summary of the i3 and i8 batteries.

http://https://wiki.aalto.fi/download/attachments/91692283/high_voltage_batteries_of_bmw_vehicles.pdf?version =1

Meaning it's better to charge at slow charge rate due to less heat being generated during charging?

[FrequentFlyer]

Originally Posted by Groundhog

Meaning it's better to charge at slow charge rate due to less heat being generated during charging?

Theoretically yes but the Thermal Management System should be up to the job with max charge rate so who knows if it makes much practical difference.

US owners get slower charging at 110V anyway if using the supplied adapter. I just set mine to the ‘Reduced’ setting and left it that way. If you really wanted to nurse the battery then you needed to precondition at least 3 hours before driving off. Any less time than this results in only the cabin being preconditioned.

For me as an Electronic Engineer it was interesting to research this stuff but as an owner I didn’t want to overthink it all. The basic rule was don’t let it bake and don’t store it for too long at full charge. Owners living in high ambient temperature climates may be looking to keep it plugged in to benefit from cooling of the battery pack as there is a trade off to be made.

[ian_i3S_iX]

I leave mine permanently plugged in, about once a week the charging system kicks into life for about half an hour. Prior to this after a few weeks of non use the battery was down to a mile or so.

I thought at first I had programmed a departure time and it was conditioning. My garage is warm if it wasn't and I could plug it in I would program a departure once a week to keep the interior fresh etc.

Interesting on views of battery tech in an i3 you get warnings of low battery charge via dash message and email with possible damage if left low, on the i8 no messages.

[FrequentFlyer]

Originally Posted by JasH

There is a significant difference between both battery types.


i3 is designed for slower discharge. i8 battery is designed for rapid charge and discharge, but with a lower output, more similar to a KERS battery.

I was told this by one of the i8 designers personally. It also makes sense, given the usage profile of the battery in each car.

Spot on. If you look at the specs then the capacity of the battery cells (back in 2014) was 60Ah in the i3 vs 20Ah in the i8 so 200% more energy but the i3’s battery pack peak discharge rate delivers barely 50% more power than the i8. It is the C-rate of the cell design that is different.

Lower C rates are better for longevity when looking at charge/discharge cycles but the SOC and Thermal degradation are the main effects for storage.