DRK002
Posts: 26
Joined: Sun Apr 22, 2018 6:05 pm

Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 8:54 am

Hello everyone

I guess we all know that it is bad for HV battery to remain in a low state of charge (SoC) for an extended period. But I’m curious as to HOW bad it is. I mean would the battery of a vehicle that has been idling at an open parking lot (at temperature of say 85 F) for 2months in less than 10% state of charge is to likely be permanently damaged? What is the threshold in this regard that causes permanent damage to the battery?
I’m talking about a 2014 BEV with a very good condition battery before this idling period. And it still shows 19.5kWh as 13.08 Batt. Kapa. Max. reading. But the SoC is about 6% and it had been sitting there like that for about 45 days at least.
Thank you

alohart
Posts: 1296
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 10:54 am

There are likely many i3 REx's that are parked for significant periods at an indicated charge level of ~6%, the REx automatic activation charge level, even though BMW doesn't recommend this. There might be i3 REx drivers who never charge and always drive with the REx engine running.

I don't believe that there is any clause in the i3 battery pack warranty that would deny warranty coverage on an i3 whose battery pack has been left at a low charge level for extended periods of time. BMW would not want to have to replace a battery pack under warranty because a REx owner left his charge level at ~6%, so significant damage probably doesn't happen under these circumstances.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

jadnashuanh
Posts: 3986
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 1:15 pm

Extremes in temperature at low charge are going to affect it more than at more moderate temperatures. For maximum life, follow the operator's manual instructions, and either leave it on charge, or at least charge it up before letting it sit. If it does get too low, and this is more true for the 12vdc battery, nothing will work until that comes up - the lead-acid, even the AGM type doesn't like low charge, and it must be functional to bring the car up. If the car is plugged in, it will keep the 12vdc battery charged as well as the main one. It will not try to charge the 12vdc battery other than when plugged in or in ready state, as far as I can tell, though.

The 12vdc battery is what maintains the run-time stuff like the alarm, comfort access, clocks, and various other bits like the cellular connection. So, like most modern cars, there is some constant but small drain on that battery. The main battery when off doesn't really have much of any load on it, and doesn't self-discharge anywhere near as fast as the AGM one, but still will. Once the main battery reaches some critical point, it won't be able to be salvaged, but I don't know where that is, and as I said, it will vary by the ambient temperature some.

IOW, you'll have less likely problems in a moderate climate than say the desert or arctic, but it will still happen. Now, if you lived in Death Valley, or Anchorage, or the northern half of the US in the winter...expect problems sooner.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

alohart
Posts: 1296
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 2:47 pm

jadnashuanh wrote:It will not try to charge the 12vdc battery other than when plugged in or in ready state, as far as I can tell, though.

My 12 V voltmeter indicates that the DC-DC converter can turn on to charge the 12 V battery when an i3 is in the operating readiness (unlock the doors) or radio readiness (turn on the entertainment system) states as well when the 12 V voltage drops below a certain level (~12.0 V as best I can tell).
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

jadnashuanh
Posts: 3986
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 3:14 pm

alohart wrote:My 12 V voltmeter indicates that the DC-DC converter can turn on to charge the 12 V battery when an i3 is in the operating readiness (unlock the doors) or radio readiness (turn on the entertainment system) states as well when the 12 V voltage drops below a certain level (~12.0 V as best I can tell).

Is that while it is plugged into an EVSE, or not?
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

alohart
Posts: 1296
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 7:06 pm

jadnashuanh wrote:
alohart wrote:My 12 V voltmeter indicates that the DC-DC converter can turn on to charge the 12 V battery when an i3 is in the operating readiness (unlock the doors) or radio readiness (turn on the entertainment system) states as well when the 12 V voltage drops below a certain level (~12.0 V as best I can tell).

Is that while it is plugged into an EVSE, or not?

Not plugged in.

I have been very surprised by how often the DC-DC converter turns on to charge the 12 V battery. When I unlock the rear hatch, the frunk, or the doors, the high-voltage system turns on and the DC-DC converter starts charging the 12 V battery if its voltage drops below ~12.0 V. It has been difficult to measure the voltage of the 12 V battery because the DC-DC converter turns on so often.

I originally thought that the 12 V battery must be very weak because of its low voltage, but the shop foreman at our BMW dealer told me that this behavior is normal. The low voltage is due to several controllers booting simultaneously which draws enough current to lower the voltage of the low-capacity 12 V battery. Because the DC-DC converter is so aggressive charging the 12 V battery, a lower capacity 12 V battery can be used compared with a normal ICE vehicle whose 12 V battery cannot be charged unless its engine is running.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

jadnashuanh
Posts: 3986
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Long Term idling in low SoC - Impact on battery

Mon Jun 11, 2018 7:11 pm

I wonder if you weren't accessing the car, i.e., it was sitting, locked, with no action trying to open it or do something, if that's the same scenario. From your description, it seems that each time you've noticed, it was when the car was being accessed for some reason.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

alohart
Posts: 1296
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Long Term idling in low SoC - Impact on battery

Tue Jun 12, 2018 11:26 am

jadnashuanh wrote:I wonder if you weren't accessing the car, i.e., it was sitting, locked, with no action trying to open it or do something, if that's the same scenario. From your description, it seems that each time you've noticed, it was when the car was being accessed for some reason.

I doubt that the high-voltage system activates while parked locked and with no external action. However, I'm not familiar with the various states that an i3 can be in other than drive readiness, operating readiness, and radio readiness. In all of these states, the auxiliary power port into which my voltmeter is inserted is powered on so that the voltmeter can be read. If other states exist in which the auxiliary power port is not powered on, the voltmeter could not be read, so I likely would not be aware of these states.

I tried to avoid depending on this voltmeter by running leads from the 12 V positive and negative terminals under the cargo compartment floor down through the bodywork exiting under the car. I could access these leads without unlocking the hatch, frunk, or doors. I connected these leads to a voltmeter and also used these leads to charge the 12 V battery with a battery charger after disconnecting the high-voltage system. I never saw voltages that would indicate that the DC-DC converter was charging the 12 V battery unless I unlocked the hatch, frunk, or doors. However, I didn't have a recording voltmeter, so I can't be 100% certain that the high-voltage system did not turn on when I wasn't monitoring the voltmeter.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

jadnashuanh
Posts: 3986
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Long Term idling in low SoC - Impact on battery

Tue Jun 12, 2018 5:56 pm

That seems to correlate to what others have seen...the 12vdc battery of cars that may sit on the lot for a long time tend to end up discharged, even if the main battery is not. But, back to the OP question...I still feel from what I've read, that it is more temperature extremes when the battery is discharged that are likely to cause problems that will be minimized if kept at a more moderate range. I'd still try to follow the manufacturer's instructions, though, and leave the car either with a full charge, or leave it on an EVSE. Unlike many other battery operated devices, the i3 does disconnect the acv input, and will not reengage it until the charge drops, or potentially during the cell balancing procedure.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

DRK002
Posts: 26
Joined: Sun Apr 22, 2018 6:05 pm

Re: Long Term idling in low SoC - Impact on battery

Wed Jun 13, 2018 10:07 am

Thank you everyone for comments ! I had not heard about -6% REXs before. Based on what you guys say i reckon the its highly unlikely that the HV battery of this car would be damaged. :)

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