MarkH
Posts: 64
Joined: Mon Jun 10, 2019 1:17 pm

Battery discharging while Stationary

Mon Mar 29, 2021 3:42 pm

My i3 had been unused while we were away for 2 months. I had connected the 12V battery to a solar panel, through a controller, to keep it charged.
When we got home, the car was dead. A cigarette lighter voltmeter showed a reading of < 10V. (This time last year, all was fine with this regime.)
I got the AA (car club roadside service) guy around and he connected a Jump-start 12V battery in parallel.
The car lit up immediately and I could do all the normal things.
HOWEVER, now, when I turn it on in the mornings, I get a message advising that the "Battery is discharging while stationary" and the %charge has dropped about 4% overnight.

It is a 2016 BEV.

Is my 12V battery had it? or is there a test I can do using a VPeake ODB device?

TARDISi3
Posts: 29
Joined: Fri Dec 18, 2020 8:46 pm

Re: Battery discharging while Stationary

Mon Mar 29, 2021 4:18 pm

sounds like you have a bad 12v battery

alohart
Posts: 2318
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Battery discharging while Stationary

Mon Mar 29, 2021 7:56 pm

MarkH wrote:
Mon Mar 29, 2021 3:42 pm
Is my 12V battery had it? or is there a test I can do using a VPeake ODB device?
That message is displayed when the 12 V battery's voltage is low. Jump-starting from another battery didn't charge your battery, so its voltage is still low. That happened to our battery. I attached a 12 V battery charger overnight and haven't seen this message again.

Your battery might be failing, but it might also only need a full charge. I would try charging it before replacing it because it might not be bad.
Aloha,
Art

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

MarkH
Posts: 64
Joined: Mon Jun 10, 2019 1:17 pm

Re: Battery discharging while Stationary

Mon Mar 29, 2021 8:33 pm

Thanks Art.
Do I need to disconnect the negative while charging? or not?

alohart
Posts: 2318
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Battery discharging while Stationary

Tue Mar 30, 2021 1:04 am

MarkH wrote:
Mon Mar 29, 2021 8:33 pm
Do I need to disconnect the negative while charging? or not?
Depends on the charger's amperage. My multistage charger charges at only 0.8 A. After an overnight charge, my charger hadn't progressed to the final stage due to the car's vampire load. After I disconnected the negative cable, charging completed within a couple of hours. I had disconnected the high-voltage disconnect prior to charging.
Aloha,
Art

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

MarkH
Posts: 64
Joined: Mon Jun 10, 2019 1:17 pm

Re: Battery discharging while Stationary

Tue Mar 30, 2021 8:30 pm

OK. Mine is on charge now. I'll see how it behaves in the morning.
My i3 number is 16-07-503 so it seems that I don't have to do the dis-connecting thing from the HV.

Just a question.
With an ICE car, the battery is recharged (after starting) from an alternator that spins while the engine is running:

How does the i3's battery get recharged when it becomes significantly discharged?
If the answer is "From the HV whenever the car is unlocked" why does it not do a full recharge using this method?
Is there no way that the car, by itself, can recover from a discharged vehicle battery?

gt6k
Posts: 3
Joined: Sun Dec 06, 2020 2:18 pm

Re: Battery discharging while Stationary

Wed Mar 31, 2021 7:46 am

The whole point of the 12v battery is to power all the systems that support the traction battery control so if the 12v is flat there is no way the car can get power from the traction battery. If it was recoverable by itself there would be no point in having the 12v battery.

MarkH
Posts: 64
Joined: Mon Jun 10, 2019 1:17 pm

Re: Battery discharging while Stationary

Wed Mar 31, 2021 12:37 pm

Sure: - if it's dead flat.
But I understand that it maintains its full charge by being topped up from the HV and this happens when any of the doors or front or back hatches are opened.
My question is, given that it can top up small amounts of normal discharge by using the HV, why can it not do a more complete recharge if the 12V becomes significantly (but not completely) discharged?

gt6k
Posts: 3
Joined: Sun Dec 06, 2020 2:18 pm

Re: Battery discharging while Stationary

Wed Mar 31, 2021 1:35 pm

If the 12v battery is worn out then it might not hold charge long enough between switchons. It probably could be arranged to continuously top up but then a fading 12v might continuously pull charge and lose it running the risk of fully flattening the traction battery which is very damaging and costly to BMWs battery warranty. Several manufacturer's BEVs seem to eat 12v batteries so its quite possibly a design choice rather than a fault.

EvanstonI3
Posts: 41
Joined: Tue Nov 03, 2020 9:11 pm

Re: Battery discharging while Stationary

Wed Mar 31, 2021 2:01 pm

MarkH wrote:
Wed Mar 31, 2021 12:37 pm
But I understand that it maintains its full charge by being topped up from the HV and this happens when any of the doors or front or back hatches are opened.
Nope. Just like an ICE car, it is just draining the 12v when you open the door and the interior lights come on. If you close the door(s) or leave them open and walk away, it times out at just under 13 minutes and shuts off the 12v power. That includes power to the 12v outlets as well. If you do anything else during that time like open another door, the timer resets. The HV battery is not "on" during this time. While the 12v cycle is "on" a fully charged 12v battery which would normally read ~12.9v when resting will show ~12.5v when it is being used by the interior lighting and whatnot. Once that cycle times out, the voltage reading goes back up to 12.9v

If you turn the vehicle "on" as in: Push the button on the stalk and put the car into "Ready" state, THEN the HV battery will kick in to re-charge the 12v. The reading at the terminals will then be just under 15vdc.
So that means it will also recharge the 12v battery while the car is sitting in Ready State or Driving.
My question is, given that it can top up small amounts of normal discharge by using the HV, why can it not do a more complete recharge if the 12V becomes significantly (but not completely) discharged?
If the 12v battery is "significantly" discharged to begin with, this is not normal.
The HV battery CAN do a more complete recharge but the 12v battery must be able to accept it.

As mentioned already it can't keep up with a worn out or shorted out 12v battery.
Some people mention smelling "rotten eggs" and find their 12v to be really hot. The battery is not holding a charge and all the energy that is trying to recharge the battery is being converted to heat instead.

The battery might also charge to 12.9vdc but if left to sit, it may self-discharge over a short period of time but the HV will apparently come on once it reaches a certain threshold and bring it back to 12.9vdc without any other intervention.
This would explain why some people have reported that their HV battery has "mysteriously" discharged by a few percentage points overnight or over a few days time and then later the 12v failed completely.
2 0 1 7 94Ah B E V

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