Battery charging : Best practice

[Plug]

Can any experienced EV owners please explain what is best practice for charging the car to keep the battery in best condition over it's lifetime ?

Are there any good reference articles online about this ?

Some questions I have include

1. Is it best to reduce the ampage delivered by the charger if you don't need a fast charge ? The domestic wallbox can charge at up to 7.4kw (32A) but you can configure the car to reduce this current. Is it a significant benefit to do that ?

2. Is it best to avoid charging up to 100% if not required ?

3. Is it best to run the battery down to low charge levels before recharging ?

The only thing I could find in the handbook about this was this paragraph.

Any advice would be appreciated.

 

[ultraturtle]

In rough order of priority:

• Avoid discharging to a very low battery charge state (i.e. running it to BMW's minimum allowable charge, then waiting weeks to charge it up).
  Avoid high amperage DC quick charging when possible.
  Avoid charging to battery bank's maximum capacity (like low-end protection, BMW probably protects you from this as well)

7.4kw charging is actually a very gentle charge, far less than you get during regenerative braking, should have no ill effect on the battery bank longevity or capacity, and will probably be a more efficient way to get energy from the wall than lower amperage charging due to overhead losses.

If any of you nice European owners would not mind hooking up a ScanGuage or Torque App adapter to get a reading of actual State of Charge (SOC) BMW programs as max, min, and REx activation values, I'd really like to know.

 

[Plug]

Thanks for the help ultraturtle. My daily mileage is only going to be about 50% of the battery range so I have the opportunity to be flexible with how the car is charged.

I've just spent a couple of hours googling/reading and found some useful information online so I'm reasonably happy that I now know what is best. I'm also going to ask BMW to see if they have any advice to give about this.

 

[TomMoloughney]

Thanks for the help ultraturtle. My daily mileage is only going to be about 50% of the battery range so I have the opportunity to be flexible with how the car is charged.

I've just spent a couple of hours googling/reading and found some useful information online so I'm reasonably happy that I now know what is best. I'm also going to ask BMW to see if they have any advice to give about this.

In an ideal world you would keep your battery between about 30% and 60% charged, but that isn't really possible.

I've published articles on this topic for a variety of websites. Here is one of them that I did for BMWBLOG: http://www.bmwblog.com/2013/04/25/understanding-battery-capacity-loss/

 

[Plug]

Thanks, that was a useful read.

 

[Bunter]

In an ideal world you would keep your battery between about 30% and 60% charged, but that isn't really possible.

I've published articles on this topic for a variety of websites. Here is one of them that I did for BMWBLOG: http://www.bmwblog.com/2013/04/25/understanding-battery-capacity-loss/

Thanks for that link Tom very useful. Out of interest how do you measure the observed battery capacity?

Regards

Bill

 

[TomMoloughney]

In an ideal world you would keep your battery between about 30% and 60% charged, but that isn't really possible.

I've published articles on this topic for a variety of websites. Here is one of them that I did for BMWBLOG: http://www.bmwblog.com/2013/04/25/understanding-battery-capacity-loss/

Thanks for that link Tom very useful. Out of interest how do you measure the observed battery capacity?

Regards

Bill

Two ways Bill. First by recording the beginning state of charge and the ending state of charge and using your driving efficiency for that trip (miles per kWh used) you can come up with an "available kWh" figure. Now one data point is useless, since it may not be exactly accurate, but if you do it every time you drive the car, like I do, and compile a few thousand data points, you get good data. Also, my home EVSE tells me how many kWh's it uses so I have that also. As long as I record the ending SOC before I plug in and then record the amount of kWh's used to fully charge I get a reliable figure. However that is wall to wheels, and I have to account for charging inefficiencies and also vampire draws for thermal management while charging, etc so it's a little more difficult to rely on that.

 

[Davidfromdigswell]

Thanks for a very interesting article Tom. I will be driving only about 15 to 20 miles on an average day and based on your tips will not charge up to 100% each night but will will charge only once every 3 or 4 days. I am hoping therefore that the i3 phone app will allow me to pre-heat the car during winter whilst the car is attached to the charger, without actually setting it to charge the batteries?

 

[oldbillygoat]

The i3 will not be available in my area, at least not for a couple of years, but I too was planning on only charging every two or three days, but hoping to still be able to precondition the batteries and heat the cabin. I hope someone can answer David’s question.

 

[Bunter]

It's not a big deal if you draw a charge for 15 minutes while the cabin pre-warms is it?

Bill

 

[Davidfromdigswell]

It's not a big deal if you draw a charge for 15 minutes while the cabin pre-warms is it?

Bill

Bill I am sure you are right and my concerns are probably just a reflection of my lack of understanding of what functionality is provided by the phone app in terms of how much control one has over the wall box. If you can plug in the car in the evening and set it to charge only for only the duration of the pre-warming the next morning, then that would be great.

David

 

[i3me]

It's not a big deal if you draw a charge for 15 minutes while the cabin pre-warms is it?

Bill

I've pre-heated this past week without the car plugged in and a complete pre-heat (first the batteries, then the interior gets done) took 7% of my battery capacity.
If you can live with that, then you don't need to plug it in!

 

[Bunter]

I've pre-heated this past week without the car plugged in and a complete pre-heat (first the batteries, then the interior gets done) took 7% of my battery capacity.
If you can live with that, then you don't need to plug it in!

Nice, that's the other way of looking at it . How long is it taking to pre-warm?

Bill

 

[i3me]

Nice, that's the other way of looking at it . How long is it taking to pre-warm?

Bill

It's toasty warm after 10min and it shuts down automatically if you don't drive the car, I believe, after 20 minutes.

 

[rclams]

It's toasty warm after 10min and it shuts down automatically if you don't drive the car, I believe, after 20 minutes.

I understand that the cabin could feel warm in 10 minutes (the air if not the materials) but I can't imagine that 22kWhr of batteries are anywhere near "warm" or even pre-warmed in 10 minutes after a long night at below freezing temperatures.

How could the warmings be sequential if the cabin is ready in just 10 minutes? :?:

 

[i3me]

It's toasty warm after 10min and it shuts down automatically if you don't drive the car, I believe, after 20 minutes.

I understand that the cabin could feel warm in 10 minutes (the air if not the materials) but I can't imagine that 22kWhr of batteries are anywhere near "warm" or even pre-warmed in 10 minutes after a long night at below freezing temperatures.

How could the warmings be sequential if the cabin is ready in just 10 minutes? :?:

What I've seen and heard on my i3 when the pre-warming sequence is started is that a fan-like noise comes from deep under the car's front end. At that time the cabin heater is not yet on and produces no heat. After 5 minutes the cabin heater engages and blows warm air into the interior, at the same time the noise at the front is reduced but does not stop completely. I interprete the first as being the start up of the battery heating and when a critical level of warming is achieved, that is trimmed to allow the cabin heater to draw current. I do not have the Heat Pump as an option, unfortunately!
When pre-heating, the ambient temp was around 7C (48F) which certainly will shorten the warm up time.

 

[simonb]

Can the REX model preheat without being plugged in? or is it just the BEV