I have purchased and installed volt meters to beneath center dash. What reading determines that there may be an issue with the 12v battery capacity. I am assuming that if the reading dropped below the designated level we would expect it to improve after taking a longer drive considering the kids each work about 2 miles from home. If the battery reading did not improve my guess is that we truly have an issue. Thoughts please.
12 volt battery in later i3s--watch out
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installing a plug-in voltmeter there is not a reliable method of determining the health or capacity of the 12v battery as they are not active after 15 minutes when the car is shut down.
the best method I have found for monitoring the behavior of the 12v battery is to install a Bluetooth 12v Battery Monitor on the Battery Terminals.
This is really the only way to see the behavior of the battery over time. When the 12v fails, it does so by self-discharging faster and faster over time. The car's DC-DC converter will come on by itself to boost the 12v battery for exactly One Hour if the battery voltage reaches 12.0 volts. You will not see this in a plug-in voltmeter.
This is what a failing 12v battery looks like when the car is simply sitting for 24hrs without being driven:
alohart
Well-known member
Totally agree except that I have seen automatic 12 V battery charging start when the battery's voltage decreased to between 12.0 V and 12.5 V. I have attached a log of the failing 12 V battery in our 2019 i3.installing a plug-in voltmeter there is not a reliable method of determining the health or capacity of the 12v battery as they are not active after 15 minutes when the car is shut down.
the best method I have found for monitoring the behavior of the 12v battery is to install a Bluetooth 12v Battery Monitor on the Battery Terminals.
This is really the only way to see the behavior of the battery over time. When the 12v fails, it does so by self-discharging faster and faster over time. The car's DC-DC converter will come on by itself to boost the 12v battery for exactly One Hour if the battery voltage reaches 12.0 volts. You will not see this in a plug-in voltmeter.
This is what a failing 12v battery looks like when the car is simply sitting for 24hrs without being driven:
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John O'Malvern
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Is this what you meant to write? I don't understand it.
McDuff
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Yes it is
The battery is not easily accessible for attaching a charger (apart from the possible harm to the electronics which I didn't know about before I posted), so I wondered if there were charging terminals easily accessible. My BMW X3 has its battery in the bottom of the boot (trunk), not easy to access, but I can charge it with the terminals in the engine compartment which are easy to get to.
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It is coming on at exactly 12.0 volts in the log you posted.
John O'Malvern
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Because you said:Yes it is
I haven't found a way to charge the 12v battery with a charger
and then said
... with which I can charge the 12v battery
Which was contradictatory.
Maybe you meant that you couldn't [easily] *until* you realised there were terminals in the engine compartment?
Sorry to be so pedantic.
alohart
Well-known member
Yes, and attached is a log showing another automatic 1-hour 12 V charging session that began at 12.5 V. I have also seen this occur at voltages between 12.0 V and 12.5 V. I wish I could find documentation that explains this automatic 12 V battery charging.
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Gonville
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This is very interesting. Our view in the UK was that the 12v was only charged if the car was ‘on’ or being charged. This seems to show some activity similar to the Tesla which wakes to condition the 12v (hence resulting in phantom drain). If this is happening for a failing 12v would we expect to see the HV SOC decline before a dead 12v? It must stop trying at some point and the 12v expire? As that seems to happen a lot over lock down and colder weather. Is this a NA adaptation?
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The 12v battery fails by self-discharging at a faster rate over time and refusing to hold a charge. At some point the DC-DC converter is unable to keep up with the 12v battery's needs and any "charging" will just turn into heat, the 12v voltage drops below some threshold where it is no longer able to operate the electronics used to operate the vehicle and the whole thing just shuts down.
Prior to this there would be odd error messages displayed and the universally dreaded "Battery Discharged While Stopped" message which is in reference the HV battery losing a charge while the car is not in use.
I tried to track this on my car when my 12v was failing to see when the car would start throwing error codes or other symptoms but gave up after first noticing the issue 2 weeks prior on my 12v BlueTooth Battery Monitor. When I swapped out the 12v battery it was being re-charged by the car every other hour. I would have liked to have let the thing go as long as possible to see how everything failed but I am not the only user of the car and I was not keen on having my wife get stranded someplace to satisfy my own curiosity.
One more mystery point regarding the 12 volt.
When mine died last year (barely a 1½ years old!) I thought there was a bigger problem. Called AAA for the tow but first we jumped the 12 volt and got the car alive, so I opted to drive it in.
Even though the HV had a good 75% charge, the %SOC display indicated 0%. But the car was running so I chalked it up to a bug, and with only a hint of trepidation set off on the 5 mile drive, sticking to local streets "just in case."
A mile from the dealership the car stopped cold, so it really "thought" it was at 0%. I was able to keep it alive while waiting for the second tow so that the parking pawl didn't engage. Dealer said it was just a bad 12 volt, nothing more, and sent me on my happy way.
I mention this in this thread because we're discussing the jump points and the converter jumping in to provide power to the 12v bus, but that there maybe be additional factors to consider when trying to revive a failed battery.
When mine died last year (barely a 1½ years old!) I thought there was a bigger problem. Called AAA for the tow but first we jumped the 12 volt and got the car alive, so I opted to drive it in.
Even though the HV had a good 75% charge, the %SOC display indicated 0%. But the car was running so I chalked it up to a bug, and with only a hint of trepidation set off on the 5 mile drive, sticking to local streets "just in case."
A mile from the dealership the car stopped cold, so it really "thought" it was at 0%. I was able to keep it alive while waiting for the second tow so that the parking pawl didn't engage. Dealer said it was just a bad 12 volt, nothing more, and sent me on my happy way.
I mention this in this thread because we're discussing the jump points and the converter jumping in to provide power to the 12v bus, but that there maybe be additional factors to consider when trying to revive a failed battery.
Mine also went dead few weeks ago. It will be the first battery change of my i3s '18. Five years lifetime is acceptable but I wish there was a warning for replacement before causing any trouble. The car suddenly started to show all kinds of warnings & could not run it for a while... Now I am waiting the battery to be imported...
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It is a TORX 30 so the HEX equivalent is 1/4"
I can relate to this. My 2018 i3 is now on its 4th 12v battery. I only have about 20,000 kms on it and the dealer says that is the reason the batteries are not lasting.
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