How often to recharge?

[mlsstl]

First time poster here. We are considering an i3 to replace our Mini Clubman. In looking at our lifestyle, we are mainly urban drivers -- I've got a 7 mile round trip to work and drive maybe 30 miles a day at most, while my wife has averaged 25 miles a day over her last 5 years in the Mini. (And our other car is a Subaru Outback, so we are well equipped for our road trips.)

I've looked around the forum and haven't seen this question specifically addressed, so apologies if it is a repeat.

If the car has been driven lightly on a given day and still has plenty of range for the next day or two's anticipated outings, is it better to go the extra day or two without recharging or is it OK to do nightly? With batteries, I'd like to maximize its long-term life. I'm trying not to to get hung up with old beliefs about the batteries used in these cars.

 

[Sparky]

I've read posts about trying to maintain the charge level between to points, but I don't bother. I plug in my car after every outing so I know I've got full range. Btw, mine is a rex, but I still always charge.

 

[cove3]

Everything I've read said to keep the charge between 20-70% unless you need the full range for a trip the next day. This presumably will maximixe the life/capacity

Ron

 

[justanotherdrunk]

I've read posts about trying to maintain the charge level between to points, but I don't bother. I plug in my car after every outing so I know I've got full range. Btw, mine is a rex, but I still always charge.

+1

 

[jadnashuanh]

The car automatically prevents you from fully charging the batteries, and won't let you fully discharge them...personally, I don't worry about it finding the warranty and the ability to have the maximum range available, should my plans change. Also, if you have it plugged in, you can condition the interior (and batteries if you want) so the car is comfortable when you get into it without compromising range. This can be a big thing if you live where it gets quite cold in the winter. The ONLY way to condition the batteries is to have it plugged in and set a departure time greater than 3-hours from the current time. When doing that, you can also have it precondition the interior.

 

[I33t]

+1

My daily range is similar, maybe a bit less. 30-50km and a few days a week with short 10km or no trips.

I charge to full, then I don't recharge it until I know my range is getting close to my next days trip. If I'm not sure of my trip tomorrow and my battery level is under 50%, I charge it anyway so I don't have a concern about range.

Charging to 70% would be reasonable for my use, but there is no automated method for this on the car or charger. It would mean more frequent charging for my use though. BMW makes no mention of it in the manual, but they reserve some battery capacity to protect the battery from overcharge or depletion. I think if it was important for the i3 battery, they would have made these allowances, they haven't.

To make it easy to charge to 70%, you'd need charger control. I think the top model Juicebox would be the only one with this capability. You'd have to work out how many KWh it will take to bring the i3 up to 70% and then dial that into the Juicebox. No way I'm getting up at silly hours in the morning to turn off the charger at 70%!

Unless BMW make provisions in the software to limit charging to 70% capacity I can't see a reasonable user-friendly way of implementing it, so even though it appears to be a reasonable idea I'm passing on that one.

 

[nowtta60]

A rough workaround to this is set the time to use off peak charging - and tell it off peak starts a hour before you leave. On a 7kW charger - you'll get about 7kWh in 1 hours charging ;-)

Personally at the weekend I don't bother plugging in as I only do about 50 miles here and there, but Sun-Thu night is a full charge with precon for an early start on cold mornings

 

[I33t]

A rough workaround to this is set the time to use off peak charging - and tell it off peak starts a hour before you leave. On a 7kW charger - you'll get about 7kWh in 1 hours charging ;-)

And if I don't know when I'll be leaving? Or if I need more than an hour to bring it to 70% I have to faff about in the menus on a frequent basis?

Nope

 

[mlsstl]

Thanks for the comments. Sounds like, with the battery overcharge and run-dry protection that BMW has built in, the best route is just to charge the car when one has the opportunity to use a plug and not worry any further about it.

 

[MikeS]

Thanks for the comments. Sounds like, with the battery overcharge and run-dry protection that BMW has built in, the best route is just to charge the car when one has the opportunity to use a plug and not worry any further about it.

+1

 

[Jeffj]

Thanks for the comments. Sounds like, with the battery overcharge and run-dry protection that BMW has built in, the best route is just to charge the car when one has the opportunity to use a plug and not worry any further about it.

++1

 

[Lincsat]

I use the off-peak charging that often fails so I always plug in when the charge is less than about 80% and don't need to worry if the charge fails. If over the 80%, then I don't even bother to plug in.

 

[Tomasz]

Everything I've read said to keep the charge between 20-70% unless you need the full range for a trip the next day. This presumably will maximixe the life/capacity

This is OWT (Old Wife Tale.). While it is true that Li-Ion batteries like to be kept less than full and never discharged below certain level keep in mind that for an Li-Ion cell full means 4.2V per cell and empty means about 3.2V. your BMW is equipped with sophisticated battery control module that will never allow you to reach those levels. While exact levels are unknown, I doubt it will ever charge a cell above 4.1V (all other EV manufacturers stop at 4.1V) and and it'll never allow you to discharge below ~3.3V. Which keeps you in the magic 20%-90% range for the cell.

Also your dash meter shows you % of available power, not true battery capacity - e.g. 100% means that your battery is charged to 4.1V per cell (so it's actually charged to about 90%) and 0% means that the battery is discharged to it's cut off level (so it still retains about 20% of capacity buffer).

Bottom line - follow the BMW's own manual and charge as often and as high as you want/can, the car won't let you damage it's battery.

 

[alohart]

This is OWT (Old Wife Tale.)./quote]
Not really. When nearing full charge, there is no magic charge level above which battery cell damage occurs and below which no damage occurs. Similarly, when nearing full discharge, there is no magic charge level below which damage occurs and above which no damage occurs. It's a continuum.

Chevrolet chose to set its Volt's battery pack charge level range to be smaller than that of the i3 and most (all?) other BEV's. Reducing the charge level range reduces driving range while increasing battery cell longevity as well as providing a buffer that could be used when the inevitable battery cell degradation has occurred. Chevrolet could afford to give up some range because of its full functionality REx unlike the i3's REx.

BMW doesn't want to have to replace i3 battery packs under warranty, so BMW's calculation was to set the charge range of the i3's battery pack low enough to insure that most battery packs don't degrade fast enough to require replacement under warranty but not so low that driving range would be reduced unacceptably. I doubt that BMW cares very much about what happens to i3 battery packs after the warranty expires unlike those of us who might want to keep our i3's more than 8 years.

So for those of us who don't need to push the maximum range of our battery packs and who care about battery pack longevity, controlling the battery pack charge range that we typically use will almost certainly improve the longevity of our battery packs as the Old Wife told us.