How to leave the battery while going in hollidays

[sibumi]

Hi, I am going to leave the car parked for 14 day how charged should I leave the battery?
Thank you

 

[EvanstonI3]

Ideally fully charged, but almost any level above maybe 40% would be fine. You will only have an issue if your 12v fails (or is currently failing) during those 14 days.

 

[sibumi]

Oh I am surprising, I think I read here that the battery shouldn't be left fully charged for longtime.
What can I do about the 12v battery if I don't use the car for two weeks? Thanks

 

[mojo]

For two weeks, it would be better to leave it at (say) 60% charged, than at 100%. My car is often left for up to 2 weeks and I never see more than 1 or 2% loss in HV battery in that time. As long as the 12V battery is in good shape, it will be fine. If you have doubts about the 12V battery (e.g. if it is 5 years old or more) then I would change it for a new one as a precautionary measure.

 

[groovyboovy]

I think they suggest between 60% to 80%, not near 0% and not 100% especaily if it is a hot parking location

 

[Bimmer333]

For two weeks, it would be better to leave it at (say) 60% charged, than at 100%. My car is often left for up to 2 weeks and I never see more than 1 or 2% loss in HV battery in that time. As long as the 12V battery is in good shape, it will be fine. If you have doubts about the 12V battery (e.g. if it is 5 years old or more) then I would change it for a new one as a precautionary measure.

I agree. There should be no issues with any battery as long as your 12 volt battery is in good condition. At one point, I left my 2017 i3 BEV for one week. I knew my 12 volt battery needed to be replaced soon since it was almost 5 years old but but it was currently causing me no issues up until I left my car for one week almost fully charged. When I came back one week later, it was obvious the 12 volt battery was going dead since it was causing all sorts of errors, reduced driving responses, etc. I quickly bought a new 12 volt battery from my local BMW dealership ($199 battery + $400 for installation!) I skipped the installation and installed my new 12 volt battery myself thus saving me $400! Registered the new battery on my Bimmer code and now my i3 runs perfectly again!!

Just fyi...I have run my BEV for over approximately (+/-) 10 miles when the battery gauge shows zero battery charge! I'm curious what and/or if there is a "reserve" amount of charge left when it shows zero charge??? Does anyone any insight in this issue? I'm intrigued.

 

[mojo]

There is both a top and bottom buffer built-into the i3's battery pack - so when it shows as 100% it is not quite fully charged, and when it shows 0% it is not fully depleted.

However, the bottom buffer is not a "reserve" as such. It is there to ensure that the cells themselves never go below a minimum charge level. It is not designed to actually be used. However... you can use some of it because (I am told) once you get to 0 miles left, the charge sector elements on the right of the dash display start to go out, and power availability reduces (i.e. it enters what other manufacturers call "turtle mode").

 

[alohart]

I try to avoid parking our i3 for longer than a day at a 100% displayed charge level (~95% actual charge level) because doing so accelerates the battery cell degradation rate, especially during our warm weather. When an i3 is off, not charging, and not preconditioning, its battery pack is disconnected from the HV circuit, so no HV loads will discharge it. It does slowly self-discharge (~1%/month in my experience), but not enough to be of concern. I have stored our i3's 8 times for periods of 3 to 9 months each time with the charge level 40%-60%. The charge level has never decreased more than a few percent while stored.

The 12V battery can be of concern because always-on 12V loads and self-discharge will discharge it (e.g., keyless entry system, telematics module, burglar alarm). As others have written, if your 12V battery is in good condition, it should last for over a month. Some i3's or some system software levels support automatically charging of the 12V battery for 1 hour when its voltage decreases below a certain level. However, this behavior doesn't seem to be documented, so I never count on it even though my 12V system logger has recorded such behavior on several occasions. So for storage longer than 1 month, I always disconnect the negative cable of the 12V battery to prevent it from being discharged. This has never caused a problem when taking our i3's out of storage.

Just fyi...I have run my BEV for over approximately (+/-) 10 miles when the battery gauge shows zero battery charge! I'm curious what and/or if there is a "reserve" amount of charge left when it shows zero charge???

The displayed charge level is a calculated estimate that can't be directly measured. As a result, it can be a bit inaccurate although the battery management system (BMS) calibrates its estimate when the battery pack voltage reaches the maximum or minimum value allowed by the BMS.

Some i3 owners have reported running out of charge when the displayed charge level was >0%. Others have reported being able to continue driving at a displayed charge level of 0%. There is no official reserve but a "reserve" might exist if one is lucky. I certainly don't count on a reserve existing. Instead, when the charge level is very low, I pay close attention to the power gauge (attached image). If the gray ePOWER segments begin disappearing starting in the upper right, the charge level is so low that the climate control power will be automatically reduced and one's speed should be reduced to increase the remaining range.



I periodically drive down to a displayed 0% charge level to help the BMS calibrate its charge level estimate and to learn whether the displayed charge level might be too high. I have never run out of charge while the displayed charge level is >0%, but I have not been able to drive very far at a displayed 0% before power starts being reduced.

 

[Dutchi3]

I periodically drive down to a displayed 0% charge level to help the BMS calibrate its charge level estimate

For an older i3 that may not be a good idea, because when you have a weaker cell or cells in your pack after many years, those may experience too much undervoltage and you may damage them over time. I am not shure if the bms takes that into account but I try to keep the discharge above 10%, preferably 20%. When my car was newer, I could still drive for a few miles being at zero charge but in the end, only creep mode for a few hundred yards... happened only once and I made it to the charging station. I won't try that now however.

 

[Bimmer333]

I try to avoid parking our i3 for longer than a day at a 100% displayed charge level (~95% actual charge level) because doing so accelerates the battery cell degradation rate, especially during our warm weather. When an i3 is off, not charging, and not preconditioning, its battery pack is disconnected from the HV circuit, so no HV loads will discharge it. It does slowly self-discharge (~1%/month in my experience), but not enough to be of concern. I have stored our i3's 8 times for periods of 3 to 9 months each time with the charge level 40%-60%. The charge level has never decreased more than a few percent while stored.

The 12V battery can be of concern because always-on 12V loads and self-discharge will discharge it (e.g., keyless entry system, telematics module, burglar alarm). As others have written, if your 12V battery is in good condition, it should last for over a month. Some i3's or some system software levels support automatically charging of the 12V battery for 1 hour when its voltage decreases below a certain level. However, this behavior doesn't seem to be documented, so I never count on it even though my 12V system logger has recorded such behavior on several occasions. So for storage longer than 1 month, I always disconnect the negative cable of the 12V battery to prevent it from being discharged. This has never caused a problem when taking our i3's out of storage.

The displayed charge level is a calculated estimate that can't be directly measured. As a result, it can be a bit inaccurate although the battery management system (BMS) calibrates its estimate when the battery pack voltage reaches the maximum or minimum value allowed by the BMS.

Some i3 owners have reported running out of charge when the displayed charge level was >0%. Others have reported being able to continue driving at a displayed charge level of 0%. There is no official reserve but a "reserve" might exist if one is lucky. I certainly don't count on a reserve existing. Instead, when the charge level is very low, I pay close attention to the power gauge (attached image). If the gray ePOWER segments begin disappearing starting in the upper right, the charge level is so low that the climate control power will be automatically reduced and one's speed should be reduced to increase the remaining range.

View attachment 1395

I periodically drive down to a displayed 0% charge level to help the BMS calibrate its charge level estimate and to learn whether the displayed charge level might be too high. I have never run out of charge while the displayed charge level is >0%, but I have not been able to drive very far at a displayed 0% before power starts being reduced.

Good information. Thank you!

 

[Bimmer333]

There is both a top and bottom buffer built-into the i3's battery pack - so when it shows as 100% it is not quite fully charged, and when it shows 0% it is not fully depleted.

However, the bottom buffer is not a "reserve" as such. It is there to ensure that the cells themselves never go below a minimum charge level. It is not designed to actually be used. However... you can use some of it because (I am told) once you get to 0 miles left, the charge sector elements on the right of the dash display start to go out, and power availability reduces (i.e. it enters what other manufacturers call "turtle mode"

 

[Ridingmore]

We've just returned from 4 months away - left our 2017 94ah Rex at ~60%, and 4 months later it was no more than a couple of percent under that - easy! Obviously you will want to turn off A/C and the likes which will drain your battery in a matter of days if left activated.

 

[alohart]

We've just returned from 4 months away - left our 2017 94ah Rex at ~60%, and 4 months later it was no more than a couple of percent under that - easy! Obviously you will want to turn off A/C and the likes which will drain your battery in a matter of days if left activated.

If you left your 12V battery connected, automatic 12V battery charging must have charged the battery periodically. I doubt that even a healthy 12V battery could withstand 4 months of always-on 12V loads without discharging so much that an i3 wouldn't start.

I wish I understood what triggers automatic 12V battery charging and whether it depends on an i3's age or integration level. We'll be away for 4.5 months in 2025 but I don't trust automatic 12V charging to keep our 12V battery healthy, so I'll do as I've always done and disconnect its negative cable.

 

[Ridingmore]

If you left your 12V battery connected, automatic 12V battery charging must have charged the battery periodically. I doubt that even a healthy 12V battery could withstand 4 months of always-on 12V loads without discharging so much that an i3 wouldn't start.

I wish I understood what triggers automatic 12V battery charging and whether it depends on an i3's age or integration level. We'll be away for 4.5 months in 2025 but I don't trust automatic 12V charging to keep our 12V battery healthy, so I'll do as I've always done and disconnect its negative cable.

I assume the 12v loads must be really low (without A/C on obviously), because I too was a little trepidatious about leaving it that long, but clearly it worked om, at least on this occasion. I guess I've read on these threads the challenges that some have had when changing their 12v battery, and are surprised that simply disconnecting the negative terminal of the 12v battery doesn't create the same symptoms. Are there any other precautions you take, or is that it? Thanks in advance

 

[alohart]

I've read on these threads the challenges that some have had when changing their 12v battery, and are surprised that simply disconnecting the negative terminal of the 12v battery doesn't create the same symptoms. Are there any other precautions you take, or is that it?

I think the secret is to try to keep the 12V system voltage either at 0V or above ~12.0V (I don't know the voltage limit below which problems can occur). Low, non-zero voltages seem to result in many spurious diagnostic trouble codes (DTC's) being stored which can cause problems until they're deleted with an OBD scanner or the 12V and HV systems sort things out on their own when an i3 sleeps. Nothing can happen at 0V including storing spurious DTC's, so 0V doesn't cause any problems.

 

[drcarrera]

I keep my non-electric cars on a (C-TECH) 12V battery conditioner if they're left for a long time. Can't the same not be done on the i3?

 

[alohart]

I keep my non-electric cars on a (C-TECH) 12V battery conditioner if they're left for a long time. Can't the same not be done on the i3?

Yes. However, BMW's procedure includes disconnecting the HV disconnect first so that the i3's DC-DC converter can't turn on to charge the 12V battery at the same time. If the output voltage of the battery conditioner exceeds that of the DC-DC converter, current could flow backward into the DC-DC converter which might risk damaging the most expensive electronic module in an i3. This risk is likely pretty low, but why risk a very expensive repair which disconnecting the HV disconnect could prevent this from happening?

 

[drcarrera]

Yes. However, BMW's procedure includes disconnecting the HV disconnect first so that the i3's DC-DC converter can't turn on to charge the 12V battery at the same time. If the output voltage of the battery conditioner exceeds that of the DC-DC converter, current could flow backward into the DC-DC converter which might risk damaging the most expensive electronic module in an i3. This risk is likely pretty low, but why risk a very expensive repair which disconnecting the HV disconnect could prevent this from happening?

Thanks. As you say, not worth the risk, then!

 

[mojo]

If you're using a CTEK charger, I would think that the probability of causing any damage to other electronic components is very low. They have a very good reputation. I probably wouldn't risk it with a cheap Chinese unheard of brand.