Is there a BMW recommended charging regime?

[DerfSdrawd]

Following my range test to destruction http://www.mybmwi3.com/forum/viewtopic.php?f=10&t=854 I asked my local dealer if BMW recommends a charging regime, for example should we keep it topped up, deplete it from time to time or what?

The reply was:
"BMW don’t recommend anything in particular regarding the battery other than charging it when you have chance as some charge in the car is better than without any charge. You don’t need to run the battery completely flat for charge indicator accuracy. It is also good for you to get into a habit of charging your BMW i3 when you can."

So there you go. And as I noted in the post linked above, BMW seems to monitor the SOC anyway so they can tell if a battery is being abused. #bigbrother

Fred

 

[SanSerif]

I asked my dealer about this when I collected the car. His advice was to just plug it in whenever I got the chance and drive it just like a normal car; no strategies, policies or regimes needed.

I'm still not sure whether this is just a reassuring platitude for nervous EV neophytes or whether BMW have engineered the need for regimes out of the system.

 

[mindmachine]

I own a Toyota plug-in Prius and Toyota actually recommends not charging the battery to full and leaving it sit for long periods of time. They recommend charging with the timer so that it is just reaching full charge around the time you are ready to depart. They also don't recommend leaving it with a real low state of charge. It would seem that battery life is the main reason, and it is further implied that it is best to leave them at about 60 to 80% SOC when not in use for any period of time.


There is a lot of discussion about battery charging and what SOC is best for obtaining the best battery life. Apparently battery misuse and abuse like running them down to nothing, and fully charging them and then not using them for several days is very detrimental to battery life. I t was further suggested that this behavior will reduce your batteries ability to hold as much charge and thus impacts (reduces) the capacity over time. While battery capacity is reduced gradually with each successive recharge, abuse reduces the battery capacity much faster than normal recommended use protocols.

Hope this helps you.

Oh I forgot, the Nissan Leaf also has guidelines somewhat similar suggestions, but I have not actually been on their blog to read anything directly about their recommendations. The Leaf batteries protocol was discussed on the Prius chat web site and that is where I got this info.

Link to Prius chat: http://priuschat.com/f/toyota-prius-plug-in.105/

 

[viking79]

If the battery is Lithium Ion, for longest life you won't want to fill it to full capacity, but full capacity will give you best range. First and foremost go with what is convenient to you.

I live about 5 miles from work and would probably put around 10 to 20 miles a day on. For this reason I would try to keep it about 50% capacity.

I think US model just charges fully, so would probably put it on a timer and have it turn off after 1 hour or something (whatever works to get it to 50% capacity).

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Look at 25 C (77 F), if you store your car at that average temperature for a year fully charged, the battery has lost (permanently) 20% of its maximum capacity, but if you were at 40% charge it has only lost about 4%. Doing the math after 10 years losing 4% per year and you are at 66% of your original capacity (range 66 miles instead of 100 miles), but losing 20% for 10 years and you are at only 10% battery capacity remaining (your battery would be shot, range of only like 10 miles or less).

This is a pretty reasonable temperature. So your battery life might be extended by several years running it around 50% instead of 90% charge.

Also, I would be discharging around 10-25% a day, so the estimate is around 2000 to 4700 cycles, that would be approximately 6-16 years if I drove 300 days a year.

These numbers are just estimates, and could vary based on other factors, but Nissan/Toyota recommendations are accurate for Lithium type batteries based on what I have read from other sources.

Again, if you are driving 60 miles a day you are going to want it fully charged over night, but you will probably wear out the battery from cycling it a bunch before you run out of capacity from storing it fully charged, so I think it would really depend on what your usage profile is with how much energy you store in the battery.

Sorry, multiple edits to this

Eric

 

[ultraturtle]

The extra bucks you pay for an electric BMW buys you better battery technology than other EV offerings, which helps mitigate concerns about not only battery life, but specific energy and performance. The BMW i3 NMC chemistry kicks ass compared to the LMO technology of the Tesla Model S, Nissan Leaf, and Chevy Volt. From Battery University (http://batteryuniversity.com/learn/article/types_of_lithium_ion):

BMW NMC Technology:

Tesla, Volt, Leaf LMO Technology:

 

[jtk7]

I'm very curious about this. I currently drive a Chevy Volt and they have done a great job at making the car idiot proof when it comes to the battery. I.e. they don't allow you to "overcharge"/"top off" the battery (as i understand it)... you only use a small fraction of the pack. So it doesn't hurt to always plug the car in because they've accounted for the issue.

I don't get the same clarity from BMW. I expect to order an i3 when my lease is up next year, but I'm confused. I know w/ a Leaf they say to only charge to 80% (effectively reducing your usable range if you treat the battery right). All I've learned is that the pack is roughly 22 kWhr and has a usable amount of 18.8 kWhr. Is this buffer spread between the top and bottom of charge or all on the bottom?

Given the premium over the Volt, I would like to think BMW has handled this and the usable battery (18.8) is situated so topping off is not a problem. Wish someone could get a direct answer from BMW engineers. I wouldn't trust local dealers to have a clue.