BMW may have to up the ante soon...

[jadnashuanh]

BMW warrants their battery at a certain capacity for 8-years...there are essentially no mass-market EVs out there that have been around that long. Now, many people change their cars like shoes, but some people keep them for a long time. It will be interesting to see how things eventually hold up. The battery cells in an i3 are huge in comparison to those in the TEsla, which are very similar in size to an AA battery...just thousands of them. Even at a 0.1% failure rate, the odds of one failing in a TEsla is MUCH higher than one in an i3, and the i3's are designed in modules to be able to be replaced easily.

Anyone have a good feel on what the SOC on one of the original Teslas compared to a new battery pack? No manufacturer makes public their warranty claims issues, so we may never know except in passing from owners. ANd, that source often isn't all that reliable, as you tend to only hear from people that had issues, not those whose is and has been running fine.

 

[michaelbmw]

Idaho National Laboratory is doing detailed studies of long term battery degradation in a wide variety of EVs.

http://avt.inl.gov/fsev.shtml

They have four BMW I3s in their fleet. So far they have only about 4000 miles logged and see approximately 3% capacity loss (some more, some less). This is about typical of the other brands as well. 2013 Nissan Leafs are also down about 3% at 4K miles and 14% at 12K miles.

So very very roughly 12%/year, assuming 1000 miles/month.

 

[jadnashuanh]

If that proves to be consistent throughout the life, BMW might not be eating a lot of battery replacements since they guarantee at least 70% capacity at the end of 8-years, but it sounds like it might be close!

That curve may not be linear, though, and the Nissan verses the i3 use a different formula.

Personally, my daily need isn't much, so while I'd like not to lose a whole bunch, the car would still be useful with a fairly significant loss in battery capacity. Time will tell.

 

[RJSATLBA]

Idaho National Laboratory is doing detailed studies of long term battery degradation in a wide variety of EVs.

http://avt.inl.gov/fsev.shtml

They have four BMW I3s in their fleet. So far they have only about 4000 miles logged and see approximately 3% capacity loss (some more, some less). This is about typical of the other brands as well. 2013 Nissan Leafs are also down about 3% at 4K miles and 14% at 12K miles.

So very very roughly 12%/year, assuming 1000 miles/month.

I haven't been monitoring the battery capacity via the hidden menu but I'd be gobsmacked if it has lost anywhere near the implied percentage in 11 months and 14k miles. Anecdotally it feels 'as new'.

 

[mindmachine]

Idaho National Laboratory is doing detailed studies of long term battery degradation in a wide variety of EVs.

http://avt.inl.gov/fsev.shtml

They have four BMW I3s in their fleet. So far they have only about 4000 miles logged and see approximately 3% capacity loss (some more, some less). This is about typical of the other brands as well. 2013 Nissan Leafs are also down about 3% at 4K miles and 14% at 12K miles.

So very very roughly 12%/year, assuming 1000 miles/month.

I think your math is off slightly, 3%/4000 miles would only be 9% @ 12000 miles! 12000/4000 = 3x, not 4x if it is linear. You can't compare the two directly because of the different chemistry. Then again once the initial loos occurs it could even slow down.Llet see at that rate BMW will be replacing a lot of batteries as 30,000 miles will be at 70% or less possible even if your scenario holds.

 

[Jeffj]

3% in 12 months would be really high, and would definitely require replacing all the batteries under warranty. I'll be a lot more curious about this once they get to 1 year, 2 years, etc.

An aerospace engineer who works with batteries on space probes has stated on the Facebook group that its likely BMW will be adjusting the voltage that the batteries charge to by a couple millivolts regularly to maintain capacity. Apparently this is a regular practice with long-range batteries. Many people have reported that their battery capacity increased slightly (reported from the hidden service menu) with the software update earlier this year, lending some credence to this theory. My capacity (reported by the car) seems to have held steady between 19.4 an 19.7 kWh (you get different readings depending temperature, how long the batteries have been on the charger, how long since you've driven last, etc.) in the 9 months I've had the car.

That being said, I got a charging error resulting in a drivetrain malfunction over Labor Day weekend while the car was sitting on the charger in my garage. Its currently at the dealer awaiting a replacement "safety box" and apparently a new set of batteries. I'll try to talk to the technician directly this upcoming week when the parts arrive to get a better story. Very curious to see what my battery capacity will be after this visit.