Battery Capacity Loss

[Maplewood]

What rate of capacity loss can I expect from the i3? How does this compare to other EV's, like the Leaf or Soul?

Are there charging strategies I can use to minimize capacity loss?

 

[epirali]

What rate of capacity loss can I expect from the i3? How does this compare to other EV's, like the Leaf or Soul?

Are there charging strategies I can use to minimize capacity loss?

The i3 has much more aggressive TMS than the Leaf so it should be much more immune to heat related capacity loss. But it does not provide much controls in terms of "delayed" charging, you can mainly set a "low cost" time window that will delay the charging to that time. It basically will charge when you plug it in.

But as with almost all LiIon batteries best practice is avoid having the batteries sitting at maximum or minimum charge for extended periods of time (days/weeks not hours) and if possible not in heat. I do not believe TMS works when car is off.

 

[jadnashuanh]

The TMS will work whenever you are driving the car, and while it is connected to an EVSE (or CCS) and charging or during preconditioning if you have set a departure time. Unlike say your cellphone or laptop, once the car decides the batteries are fully charged, an EV removes the input voltage entirely. IOW, it doesn't switch to say a trickle charge mode and potentially constantly add heat.

 

[Maplewood]

The TMS will work whenever you are driving the car, and while it is connected to an EVSE (or CCS) and charging or during preconditioning if you have set a departure time. Unlike say your cellphone or laptop, once the car decides the batteries are fully charged, an EV removes the input voltage entirely. IOW, it doesn't switch to say a trickle charge mode and potentially constantly add heat.

Thanks for the great info.

So letting the car connected to the charger all night will not be harmful?

 

[jadnashuanh]

So letting the car connected to the charger all night will not be harmful?

IMHO, no. The warranty is 100K-miles, 8-years, it will hold at least 70% of new, or it will be replaced. If BMW really thought it would be a bad idea, they'd say so in the owner's manual. They spent years of field tests working on this to make it reliable. That, plus the actual chemistry used in their cells, should tolerate that with no issues.

FWIW, the charger is actually IN the car...all an EVSE is, is a smart on/off switch for the power. The car is the one that determines when it is best to actually apply power or not, and how much it wants at any one time (limited by the max it can use and what the EVSE says it has). It applies power by sending a signal to the EVSE that causes it to close the power switch (usually a contactor, a kind of relay).

 

[epirali]

So letting the car connected to the charger all night will not be harmful?

Absolutely not, the as other have pointed out the car does not "trickle charge," it shuts off. It seems to only draw from the EVSE if you precondition and that is used to run climate control, or if you pre-condition three hours before leaving to warm up the battery in cold weather for better performance. So you can plug in and leave it plugged in.

 

[alohart]

We bought our i3 BEV and plan to keep it past the battery warranty period. My take is that BMW allocated buffers at high and low charge limits sufficient to ensure that few battery packs would lose more than 30% of capacity during the warranty period and, thus, have to be replaced. But BMW didn't want to make these buffers too large because doing so would reduce already marginal range too much. I don't want our battery pack to lose possibly nearly 30% capacity by the time our battery pack's warranty expires, so I never charge to full unless I will need full range the following day. I try to maintain the charge level of our battery pack between ~20% and ~80% in hopes of decreasing the rate of capacity loss.

Only time will tell how well the i3's battery packs will age.

 

[jadnashuanh]

I've only seen a few reports, but those I have, on some of the earliest i3's delivered, have only lost a few percent after two years and in one case, nearly 50K miles, without doing any special on charging.

How the batteries are made (their chemistry), how they are protected with the i3's liquid cooling system, and the logic used to manage them seems to point to really long-term use. My sister has a nearly 14-year old Prius, and LOTS of miles...their batteries are still working fine, and the tech has gotten lots better over those years, and yes, I realize that's not exactly apples to apples comparison.