Going to out of town for a week - leave plugged in or unplugged

[CatHuxley]

Hi all,

I am new to the EV world. I just purchased my 2020 i3 last month. I'm going out of town for a week. I am wondering should I leave the car unplugged with a partial charge, unplugged with a full charge, or should I leave it plugged in.

I have a ChargePoint HomeFlex Level charger at home.

Thanks in advance for your advice.

 

[EvanstonI3]

plugged in if possible but if not it will be fine unless your 12v battery fails for some reason. We don't drive our 2017 very often and there have been times when it has sat in the garage for almost a week with a partial charge, not plugged in and we come back to it and nothing has changed.

 

[eNate]

I'm of the mind that I'd leave the car unplugged with the HV battery at a mid state of charge, but put a battery minder on the 12 volt. But not for just a week -- that's too short a time to have any worries. I definitely don't like the idea of the HV battery sitting around "topped off" for any length of time.

 

[alohart]

I am new to the EV world. I just purchased my 2020 i3 last month. I'm going out of town for a week. I am wondering should I leave the car unplugged with a partial charge, unplugged with a full charge, or should I leave it plugged in.

There are vampire 12 V loads that will discharge the 12 V battery a bit over a week just as with all modern vehicles (e.g., keyless entry system, telematics module, system clock, burglar alarm system if armed). As EvanstonI3 wrote, your 12 V battery will be fine unless it's very weak and about to die anyway.

In general, the high-voltage (HV) battery pack is disconnected from all HV loads when an i3 is turned off. Exceptions are when the doors, hatch, or frunk are locked/unlocked or opened/closed, when charging is active, when cabin or battery pack preconditioning is active, or for an hour to charge the 12 V battery when its voltage decreases beyond a certain limit. After any of these events, the HV system could remain on for as long as 30 minutes discharging the HV battery pack slightly. The self-discharge rate for Li ion battery cells is very low (~1% per month in my experience), so the charge level of your battery pack wouldn't decrease noticeably over a week.

To minimize the battery cell degradation rate on its newer EV's, BMW recommends not fully charging routinely unless maximum range might be needed. BMW might have learned from replacing many 2014-2016 i3 battery packs under warranty due to excessive cell degradation. Fortunately, later i3 battery packs seem to be much more resistance to excessive cell degradation. Unfortunately, the i3 doesn't allow its charge level to be limited when charging, so leaving an EVSE plugged in would fully charge the battery pack with it remaining at a full charge for a week. This isn't the best practice, but it almost certainly wouldn't result in enough cell degradation to be noticeable. Another concern is that a power surge could cause expensive damage to the on-board charger, so I never leave my EVSE plugged in after I finish charging.

 

[McDuff]

There are vampire 12 V loads that will discharge the 12 V battery a bit over a week just as with all modern vehicles (e.g., keyless entry system, telematics module, system clock, burglar alarm system if armed). As EvanstonI3 wrote, your 12 V battery will be fine unless it's very weak and about to die anyway.

In general, the high-voltage (HV) battery pack is disconnected from all HV loads when an i3 is turned off. Exceptions are when the doors, hatch, or frunk are locked/unlocked or opened/closed, when charging is active, when cabin or battery pack preconditioning is active, or for an hour to charge the 12 V battery when its voltage decreases beyond a certain limit. After any of these events, the HV system could remain on for as long as 30 minutes discharging the HV battery pack slightly. The self-discharge rate for Li ion battery cells is very low (~1% per month in my experience), so the charge level of your battery pack wouldn't decrease noticeably over a week.

To minimize the battery cell degradation rate on its newer EV's, BMW recommends not fully charging routinely unless maximum range might be needed. BMW might have learned from replacing many 2014-2016 i3 battery packs under warranty due to excessive cell degradation. Fortunately, later i3 battery packs seem to be much more resistance to excessive cell degradation. Unfortunately, the i3 doesn't allow its charge level to be limited when charging, so leaving an EVSE plugged in would fully charge the battery pack with it remaining at a full charge for a week. This isn't the best practice, but it almost certainly wouldn't result in enough cell degradation to be noticeable. Another concern is that a power surge could cause expensive damage to the on-board charger, so I never leave my EVSE plugged in after I finish charging.

Would you show us where that advice from BMW can be found? I’ve not found any advice from BMW about levels of charging, or indeed the best charging rates.

 

[Allenpien]

When the car is home I leave it on a level 1 charger. I am wondering if that is the best policy? My battery is rarely below 50%. So far, I have not seen any degradation of the battery. I was told that given the driving I do it is best. Is this true?

 

[eNate]

...on its newer EV's, BMW recommends not fully charging routinely unless maximum range might be needed

Would you show us where that advice from BMW can be found? I’ve not found any advice from BMW about levels of charging, or indeed the best charging rates.

If you're referring to Art's comment about BMW's current EVs, I'm sure you can pull it up in an online i4 owners manual to verify what was posted in the screenshot below, or refer to BMWs "how to" videos, or refer to the advice they give in their app (screenshot below).

If BMW were to retroactively implement selectable charging levels or an 80% recommendation in the i3, they would be opening themselves up to costly software update service campaigns and potentially litigation. They're mum on the topic – perhaps a "don't worry your pretty little head" approach to attracting EV sales – but in the same vein as what the i4 forum member wrote below, with the i3 you can justifiably stick with what BMW wrote in the manual (charge your i3 to 100%) and not make up any new recommendations. They certainly don't provide any tools to help stopping early.

 

[eNate]

When the car is home I leave it on a level 1 charger. I am wondering if that is the best policy? My battery is rarely below 50%. So far, I have not seen any degradation of the battery. I was told that given the driving I do it is best. Is this true?

It depends...

It depends on whether you're a 100% kind of guy or an 80%er. You've got to make that decision for yourself because there are arguments either way.

It depends if you're concerned about the the unlikely but real chance of a power surge damaging your voltage converter. The longer you stay plugged in beyond what's necessary, the greater the chance of being plugged in at a time when a transient voltage spike occurs, but (a) will it cause damage and (b) does it even matter if the cord is plugged in but the car has ceased charging?

Lastly it depends if you're struggling just to get enough charge because it's Level 1 and slow and you're never quite reaching your desired state of charge.

I can tell you that I charge almost exclusively Level 1 at work and if I need 15% I set the EVSE to 8 amps, if I need 30% I set the EVSE to 16 amps, and if I'm somewhere inbetween I also have 10 and 12 amps settings, even 6 amps (which I've used if I'm working a long day), and a delay start timer that's settable in 2-hour increments. My goal is to be close to 80% when I unplug at the end of a workday. I even have a trick up my sleeve to get nearly 60% in 8 hours if I really need it.

In that respect, I'm plugged in "all the time" (at work) but still try to stick to 80%.

 

[Colinh]

Our i3 has sat on our drive unplugged for two long periods. When it was a few months old it was left for five weeks during the summer. Last year (when it was 7.5 yrs old it sat for just over three weeks unplugged. Never given us any problems. Gets charged to 100% on the home 7kw charger every week or so. Still got 60 miles range in very cold weather and close to 80 in summer. Early i3 Rex. Never had anything other than routine maintenance but only got about 46k miles on the clock.

 

[McDuff]

If you're referring to Art's comment about BMW's current EVs, I'm sure you can pull it up in an online i4 owners manual to verify what was posted in the screenshot below, or refer to BMWs "how to" videos, or refer to the advice they give in their app (screenshot below).

If BMW were to retroactively implement selectable charging levels or an 80% recommendation in the i3, they would be opening themselves up to costly software update service campaigns and potentially litigation. They're mum on the topic – perhaps a "don't worry your pretty little head" approach to attracting EV sales – but in the same vein as what the i4 forum member wrote below, with the i3 you can justifiably stick with what BMW wrote in the manual (charge your i3 to 100%) and not make up any new recommendations. They certainly don't provide any tools to help stopping early.

I’ve found that 10 to 80 paragraph at last, thanks.