Long-term Storage Results

[alohart]

What type of jacks did you use and what are the contact points on the i3?

To lift our i3, I bought a lightweight aluminum floor jack and placed a BMW jack point adapter on its flat lifting surface:



To keep our i3's tires off the pavement, I used ESCO 10498 jack stand bases each with a pivot top designed to fit BMW jack points:

[Randy101]

What will be the 12v and main battery discharge rather (monthly?) if the locked car is simply left standing in place for 4 months. If I know the drain rate, i may be able to have someone do periodic charging to bring the car to 50%. With the loss of 3G I'm no longer able to remotely monitor levels.

Alternatively, if the car would be plugged for 4 months, what is the degree of harm the main battery charged at 100% will experience?

[alohart]

What will be the 12v and main battery discharge rather (monthly?) if the locked car is simply left standing in place for 4 months. If I know the drain rate, i may be able to have someone do periodic charging to bring the car to 50%. With the loss of 3G I'm no longer able to remotely monitor levels.

Alternatively, if the car would be plugged for 4 months, what is the degree of harm the main battery charged at 100% will experience?

In my experience, the high-voltage battery pack self-discharges ~1% per month during storage, so you shouldn't worry about the high-voltage battery pack discharging too much while your i3 is stored for 4 months. I store our i3 with the charge level between 40% and 60% which reduces the battery cell degradation rate compared with storing it at a higher charge level. I can't quantify the harm caused by storing it fully charged. Tests of Li-ion battery cells with chemistries similar to those used in i3's indicate that the degradation rate increases with the charge level and temperature, so why store an i3 fully charged when doing so isn't necessary?

The health of your 12 V battery would determine when it would discharge enough to either damage it or to set all sorts of DTC's as happens when a 12 V battery fails. When an i3 is locked, its burglar alarm is armed, so the burglar alarm would join the keyless entry system, the telematics module, the clock in the entertainment system, and other parasitic 12 V loads that would gradually discharge the 12 V battery. I would be very surprised if it would not be essentially totally discharged if you left your i3 parked and locked for 4 months.

That said, I know of 1 report of an i3 that sat parked for over a year yet was able to start. The owner stated that an EVSE was not plugged into his i3. He wrote that the charge level of the battery pack had decreased noticeably which led him to believe that an i3 would periodically charge its 12 V battery by turning on the DC-DC converter. I have not found any documentation that supports this. Some i3 owners have installed 12 V battery monitors that store the 12 V system voltage over time. None of these owners have reported the DC-DC converter periodically turning on to charge the 12 V battery.

So when we store our i3, I always disconnect the high-voltage disconnect under the removable cover to the right side of the frunk box before disconnecting the negative cable of the 12 V battery, both of which are quite easy to do. I then fully charge the 12 V battery with a battery charger so that its charge level remains high during storage.

There is no evidence that leaving an EVSE plugged in for 4 months would keep your 12 V battery charged. The DC-DC converter charges the 12 V battery only when the high-voltage battery is actively charging (actually, it remains on for up to 30 minutes after the battery pack is fully charged). Indeed, several i3 owners have reported dead 12 V batteries even though an EVSE had been plugged in during storage.

Having stored our i3 5 times for periods of 3 to 9 months each time, I have always been able to take our i3 out of storage without any problems. I don't think I could say that if I had left the 12 V battery connected during storage.

[JohnKelly]

Nice response, but: "so why store an i3 fully charged when doing so isn't necessary?" Because there is no such thing as a fully charged i3 battery, perhaps? I would trust the battery management software to take care of it. Of course, you might be on to something with the 12 volt battery... especially one of unknown age.

[alohart]

Nice response, but: "so why store an i3 fully charged when doing so isn't necessary?" Because there is no such thing as a fully charged i3 battery, perhaps? I would trust the battery management software to take care of it.

The U.S. i3 Owner's Manual states:

"The service center can advise you on what to consider when storing the vehicle longer than three months."

The first time I planned to store our i3 for 6 months, I asked the service manager at our BMW dealer what he recommended. He told me that the 12 V battery was of greatest concern because vampire loads would discharge it, so he recommended disconnecting the negative battery cable. This isn't unique to an i3; all modern vehicles have vampire 12 V loads that gradually discharge the 12 V battery.

He also recommended storing with the battery pack's charge level near 50%. There are no high-voltage vampire loads (the battery pack is electrically disconnected when an i3 is off), so the energy in the battery pack isn't being used during storage. The self-discharge rate of Li-ion cells is very low, so there's no concern about the charge level decreasing so low that the cells could be damaged.

I have followed his recommendations several times since with no resulting problems and with a 12 V battery that lasted over 7 years before not holding a full charge.

While a 100% displayed charge level isn't the actual charge level, for a 60 Ah battery pack, the actual charge level is ~96%. That's still quite high. The cell degradation rate of any Li-ion battery cell with a chemistry similar to that used in i3 cells increases as its charge level increases, so the degradation rate is greater at a 100% displayed charge level than it is at a displayed 50% charge level. Why would any i3 owner store her i3 at a 100% displayed charge level when energy in the battery pack isn't needed for anything during storage? If one doesn't care about maintaining one's battery pack capacity at the highest possible level over a long ownership, then by all means store an i3 at a 100% displayed charge level.

Of course, you might be on to something with the 12 volt battery... especially one of unknown age.

This is a problem with any modern vehicle that's stored. I believe that BMW disconnects the 12 V battery during shipping from its factory. Dealers are supposed to check the 12 V battery voltage periodically while a new BMW is on the dealer's lot and charge the 12 V battery when the voltage drops below a certain level. When we bought our i3 new, a checklist which included checking the 12 V battery periodically was in the glove compartment.

[Randy101]

Before disconnecting the negative connection to the 12v battery, should I using the main battery disconnect, and leave it disconnected for the duration of storage?

An on return first connect the negative 12v and then reconnect the main battery.

[alohart]

Before disconnecting the negative connection to the 12v battery, should I using the main battery disconnect, and leave it disconnected for the duration of storage?

I always back up my driver profiles to a USB flash drive prior to storing our i3. With no 12 V power while in storage, the driver profiles could be lost. I then restore the profiles after reconnecting the 12 V negative cable. You might need to set the clock afterward.

Yes, disconnect the high-voltage disconnect prior to disconnecting the 12 V negative cable. Make sure the burglar alarm isn't on (i.e., the doors aren't locked) when you disconnect the negative cable. If the alarm is armed, the siren will sound when the negative cable is disconnected which is very loud when one's head is in the frunk while disconnecting the negative cable.

When the negative cable is disconnected, the windows won't roll down when opening the doors. Be gentle closing the doors because the windows will collide with the weather stripping.

If you plan to lock the doors before storing your car, you'll need to use the physical key in the fob to lock the driver door after locking the passenger door from inside the car. Be careful removing and installing the lock cover on the driver door. If not snapped securely into place, it could fall off while driving. Buying a replacement could be expensive because it might need to be painted to match the body color.

Leave the frunk only partially closed during storage, if possible. If you close it all the way, you'll have to open it with the emergency opening cable in the driver door jamb.

It's best to let the high-voltage system go to sleep with the frunk open before doing anything else (wait 30 minutes without opening or closing the doors, hatch, or frunk). I once disconnected the high-voltage disconnect before the high-voltage system was asleep which immediately caused a drive train error. Fortunately, that error cleared when I reconnected everything, but I was concerned that I had caused a problem.

Leave the high-voltage disconnect disconnected during storage.

An on return first connect the negative 12v and then reconnect the main battery.

Yes, that's the correct order.

[Ladysman101]

I have a question about using a battery tender to maintain the 12 volt while away for 4 wks in here in the Northeast, I wanted to ask if I need to disconnect the high voltage connection to the 12 volt before adding the battery tender.. would appreciate someone here sharing their knowledge on this. Thanks.

[alohart]

I have a question about using a battery tender to maintain the 12 volt while away for 4 wks in here in the Northeast, I wanted to ask if I need to disconnect the high voltage connection to the 12 volt before adding the battery tender.. would appreciate someone here sharing their knowledge on this.

Several i3 owners who have installed 12 V battery monitors have reported the DC-DC converter turning on automatically for an hour to charge the 12 V battery when its voltage drops below a certain level. That's not likely to happen when a battery tender is connected, but who knows what unexpected situation might occur? Also, the HV system turns on when unlocking or opening a door, the hatch, or the frunk. When the HV system turns on, the DC-DC converter could also turn on depending on the 12 V battery's voltage, the i3's integration level (system software version), or maybe even model. I would not want the DC-DC converter to turn on when a battery tender is also charging the 12 V battery for fear that this could damage the DC-DC converter which is an irreplaceable portion of the very expensive EME.

It's so easy to disconnect the HV disconnect that why not do it to avoid potential expensive damage even if that's a remote possibility?