12 volt battery in later i3s--watch out

[alohart]

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.

I drove our 2014 i3 only 13k miles (21k km) over more than 7 years. Our 12 V battery lasted for more than 7 years. This is probably because we stored our i3 for a total of ~3 years during that 7 years with the negative cable of the 12 V battery disconnected so that its only discharge was self-discharge which didn't reduce its charge level too much. If my driving habits were like yours, I might install a disconnect on the negative cable so that I could easily disconnect the 12 V battery while it was parked for longer periods. That would prevent the battery from discharging so much that it's life is shortened.

 

[Gonville]

When you open the doors, the DC-DC converter comes on and charges the 12v battery. It would normally time-out at around 15 minutes but if you closed a door and opened it again, the cycle repeats. With the car OFF and not in Drive mode, I can see how doing this over 2hrs could cause the car to trigger that warning, because the HV battery is "charging" the 12v while you are doing this, AND the car is "stopped".

I've noted further up this thread what my 12v battery looked when it was failing. It was self-discharging to 12.0 volts and the DC-DC converter would come on for exactly 1 hour to "boost" the 12v battery. I never got the "Battery Discharging While Stopped" message while this was going on though.

Pretty sure it isn’t activating the DC-DC charger unless the car is ‘on’. Easy to leave it in that state but opening the door makes it go to off - of course it stays on if you clip the seatbelt in (behind you) as it still thinks you are safely in the car. So with it ‘off’ but the rear open side doors not open it 100% discharges.

 

[Gonville]

I drove our 2014 i3 only 13k miles (21k km) over more than 7 years. Our 12 V battery lasted for more than 7 years. This is probably because we stored our i3 for a total of ~3 years during that 7 years with the negative cable of the 12 V battery disconnected so that its only discharge was self-discharge which didn't reduce its charge level too much. If my driving habits were like yours, I might install a disconnect on the negative cable so that I could easily disconnect the 12 V battery while it was parked for longer periods. That would prevent the battery from discharging so much that its life is shortened.

Is this also because you have very moderate temperatures? We have below zero centigrade frequently in winter and folks routinely get a failure if they have left the car for a week at Christmas/end of year holidays. If the 12v is already weak I guess that can kill it off more frequently.

I like your graphs and have borrowed them. Hope that is OK.

 

[EvanstonI3]

Pretty sure it isn’t activating the DC-DC charger unless the car is ‘on’. Easy to leave it in that state but opening the door makes it go to off - of course it stays on if you clip the seatbelt in (behind you) as it still thinks you are safely in the car. So with it ‘off’ but the rear open side doors not open it 100% discharges.

I have a power-port voltage reader plugged in and I can clearly see when it jumps up from 12.4 to 14.8 volts. The car does not have to be "on".

 

[mojo]

Same here - mine will definitely power-on the DC-DC converter just with the door being opened, though the rules seem to be quite complex (e.g. I *think* if the battery voltage is above a certain voltage threshold it won't turn on).

It's another aspect of the car - like the detailed charging behaviour - which is complicated and not documented for the user by BMW.

 

[Dutchi3]

My i3 from 2014 with 112.000km/70.000miles is still on it's first 12v battery. I never experienced a lock-up due to a failed 12v battery, but after reading this thread, I might do well by changing the battery. If the 12v battery is kept alive by the DC-DC converter, then it might be so that I gain more range by changing the 12v battery, because then, the DC converter does not have to top-up the 12v battery that much. Sometimes I notice that the range in the morning is less than the previous evening when I park the car. This may be due to temperature differences, but also because the DC-converter is charging the 12v battery overnight. Food for thought.. can anyone relate to this?

 

[robthebold]

My i3 from 2014 with 112.000km/70.000miles is still on it's first 12v battery. I never experienced a lock-up due to a failed 12v battery, but after reading this thread, I might do well by changing the battery. If the 12v battery is kept alive by the DC-DC converter, then it might be so that I gain more range by changing the 12v battery, because then, the DC converter does not have to top-up the 12v battery that much. Sometimes I notice that the range in the morning is less than the previous evening when I park the car. This may be due to temperature differences, but also because the DC-converter is charging the 12v battery overnight. Food for thought.. can anyone relate to this?

Don't worry about the range; drive on in to get a new battery before you have to walk.

 

[EvanstonI3]

Sometimes I notice that the range in the morning is less than the previous evening when I park the car. This may be due to temperature differences, but also because the DC-converter is charging the 12v battery overnight. Food for thought.. can anyone relate to this?

Check the PERCENTAGE OF CHARGE in the evening by tapping the button on the turn signal until it appears on the dash. Then come back the next morning and see if that number has changed at all. If it HAS, then you most likely have a dying 12v battery. That's a better indicator than the Range changing.

 

[Dutchi3]

Check the PERCENTAGE OF CHARGE in the evening by tapping the button on the turn signal until it appears on the dash. Then come back the next morning and see if that number has changed at all. If it HAS, then you most likely have a dying 12v battery. That's a better indicator than the Range changing.

Good tip. Never saw the percentage of charge change significantly but I will check this. Is it possible that the 12v battery is just still fine and does not yet need a replacement?

 

[EvanstonI3]

Is it possible that the 12v battery is just still fine and does not yet need a replacement?

You say your 2014 is still on the OEM original 12v battery. If true, you are on borrowed time. You are an outlier.
Some batteries fail at 2 years. Most seem to fail at 3-4 years. A few others fail at 6-7 years.
Is the risk worth it? Only you can make that call.

 

[alohart]

My i3 from 2014 with 112.000km/70.000miles is still on it's first 12v battery. I never experienced a lock-up due to a failed 12v battery, but after reading this thread, I might do well by changing the battery.

When 2014 i3 batteries began failing in significant numbers in 2017, I bought a replacement which I stored in our apartment until the original battery failed. I rarely park anywhere for very long except where I park overnight, and I know that the DC-DC converter can remain on for 15-30 minutes after shutting off an i3 when the 12 V battery needs charging, so the risk of being stranded away from home seemed small. I continued driving with the original battery for an additional 3 years until the original battery began discharging more and more rapidly when parked (I could see this with my BM2 12 V system monitor). I then replaced the battery with the spare that I had charged 2 to 3 times per year while it was stored.

If the 12v battery is kept alive by the DC-DC converter, then it might be so that I gain more range by changing the 12v battery, because then, the DC converter does not have to top-up the 12v battery that much.

The usable capacity of even a degraded HV 60 Ah battery pack might be as low as 13 kWh. The usable capacity of the 12 V battery is 20 Ah * 12 V = 240 Wh = 0.24 kWh, only ~2% of the HV battery pack's usable capacity. Even considering DC-DC converter conversion losses, the amount of energy required to completely charge a dead 12 V battery would not reduce the HV battery pack charge level noticeably. However, a short-circuited 12 V battery would discharge the HV battery pack noticeably because the 12 V battery would be charged automatically for periods of 1 hour each time when the 12 V battery's voltage decreases below a certain level. A short-circuited 12 V battery would result in a warning message being displayed about excessive discharge while parked, so the failure of the 12 V battery shouldn't be a surprise.

Sometimes I notice that the range in the morning is less than the previous evening when I park the car. This may be due to temperature differences, but also because the DC-converter is charging the 12v battery overnight. Food for thought.. can anyone relate to this?

The DC-DC converter doesn't automatically charge the 12 V battery except under certain conditions which don't seem to be documented publicly. I've seen this happen when the 12 V battery's voltage decreased below 12.5 V but also below 12.0 V at a different time, so there must be something other than voltage that triggers this automatic recharging. Unless the 12 V battery is significantly discharged which wouldn't happen if an i3 is driven regularly with a good 12 V battery, automatic charging would not occur when parked overnight, so the HV battery pack's charge level wouldn't decrease noticeably.

 

[alohart]

Is this also because you have very moderate temperatures?

Might be. Also, our 12 V battery was disconnected for a total of ~3 years while our i3 was in storage for periods of 3 to 9 months each time. I fully charged the battery after disconnecting it, so it sat at a high charge level while disconnected and didn't experience any charge-discharge cycles which probably increased its life.

I like your graphs and have borrowed them. Hope that is OK.

Certainly!

 

[Gonville]

I just had a visit from a friend who is a power systems engineer with our National Grid. So he certainly has more electrical knowledge than I have even if it is a kVa level. He is currently driving a hybrid Ford Kuga I believe. This has been having , in the forums, a number of issues with 12v failing and it being pretty difficult to get the flap to open the hood to reach the 12v terminals there - rather than buried in the trunk where the actual battery is. So being RHD the engineering is a bit different.

Anyway it was interesting to hear him talk about updating his AGM battery by using the parameters in the FORD tool (which is configured for all models) to set the parameters for a new battery with ‘bigger’ dimensions. The bolt holes are there in the trunk and the configuration allows it to be set. He also said that the configuration had all the settings in it for LFP batteries as well so he is contemplating that when the next time the AGM passes. His car was 3 years old so just out of warranty but he was getting prepared due to the high number of incidences other users were having. Wonder if Bimmercode or others would allow us to code a correct set of charging parameters. He noted that for the AGM the voltage at the terminals was 14.8v when starting but dropped off as the AGM was charged. That doesn’t seem to be what BMW have done judging by your graphs.

By the way what tool are you using for the monitoring as I’d like to replicate your findings.

 

[alohart]

Anyway it was interesting to hear him talk about updating his AGM battery by using the parameters in the FORD tool (which is configured for all models) to set the parameters for a new battery with ‘bigger’ dimensions. The bolt holes are there in the trunk and the configuration allows it to be set. He also said that the configuration had all the settings in it for LFP batteries as well so he is contemplating that when the next time the AGM passes. His car was 3 years old so just out of warranty but he was getting prepared due to the high number of incidences other users were having. Wonder if Bimmercode or others would allow us to code a correct set of charging parameters.

I don't believe so. I could change the battery capacity and type in BimmerCode, but only from a list of choices. LFP isn't included; only flooded-cell lead-acid and AGM are included. The capacity could be changed to 40 Ah and some even large values, but nothing between 20 Ah and 40 Ah if I recall correctly. The settings apply to the Body Domain Controller (BDC) under "Battery Type" in standard, not expert, mode.

He noted that for the AGM the voltage at the terminals was 14.8v when starting but dropped off as the AGM was charged. That doesn’t seem to be what BMW have done judging by your graphs.

Correct. The DC-DC converter seems to be on at full voltage or off. That said, I have watched the 12 V system voltage vary by maybe 0.3 V while the DC-DC converter was on but haven't correlated that to the 12 V battery's charge level. This seems to be undocumented behavior as far as I know.

By the way what tool are you using for the monitoring as I’d like to replicate your findings.

I just checked the Amazon U.K. Website to verify that the BM2 battery monitor is available. Several different resellers are selling identical monitors, so just buy the least expensive one.

It is alleged that the BM2 smartphone app sends personal information including location, WiFi and cellular network information, and maybe other information back to Chinese servers. This might be more of a problem on the Android version. On iOS, I have disabled accessing location information and background app refresh for the Battery Monitor app. This app doesn't show up in apps using the most power, so I have no evidence that it's doing anything objectionable, but it certainly could be.

 

[Gonville]

A new piece of information - well history. Today one of our UK members had his alarm go off at 3am. Ordered and fitted new BMW 12v. This is on a 2014 model. This was the battery he took out. 10 years! Original BMW fitted. I have asked for information on how he looked after it seems he only ever used the brick charger which may be a factor.

 

[Gonville]

A new piece of information - well history. Today one of our UK members had his alarm go off at 3am. Ordered and fitted new BMW 12v. This is on a 2014 model. This was the battery he took out. 10 years! Original BMW fitted. I have asked for information on how he looked after it seems he only ever used the brick charger which may be a factor.

Miles 106,000 charged everyday on brick. Southeast of UK so mild. Average journey 30 miles each day and average speed 30mph city based London. So looks like a real gentle condition.

 

[Dutchi3]

Miles 106,000 charged everyday on brick. Southeast of UK so mild. Average journey 30 miles each day and average speed 30mph city based London. So looks like a real gentle condition.

As stated before, my i3 is also on it's original 12v battery. My car was always parked outside. In the Netherlands we have a fairly mild climate as well. I think the 12v battery holds up longer in mild climates and with frequent use. I think 10 years from a AGM battery that is not drained often, should be a normal life span. If the car is parked for long times very often, or if the climate is harsh, then I expect a lower life span. Still, as advised, replacing the battery in time is a better option than to wait until it dies.