BMW i3 auxiliary battery sizes

[Mito]

Apples and oranges....

Wasnt it obvious?
My whole point for this discussion, and my decision to go with a larger battery, is that if there is the slightest consumption over the normal sleep mode (0.05-0.15A) the 12v battery will go flat and it will probably be dead too. It happens, and will happen with the modern BMWs.
My car has no warranty and i have no desire to buy $170+ battery multiple times and deal with dead car recovery with my wife inside. Or rely on a tow truck driver to jump-start it To each it's own, I just share my modification and the logic behind it.

I agree after having to rescue my Mrs when the battery failed.
The 20ah battery is underspec'd and of questionable quality
A 40ah battery is cheaper and less likely to fail
All 3 of my cars have had failed batteries its an epidemic and a weak point on the car so you can learn from history or be doomed to repeat it, your choice...

 

[alohart]

The 20ah battery is underspec'd and of questionable quality

Of questionable quality, maybe. Maybe that explains your repeated 12 V battery failure.

Underspec'd, almost certainly not. Since driving with a voltmeter in the center auxiliary power port, I've noticed that the DC-DC charger is almost always charging the 12 V battery, not only when driving, in effect adding the capacity of the Li-ion battery pack to the 12 V system. But unlike in an ICE vehicle, there's no slow starter motor to indicate that the 12 V battery is failing, so i3's 12 V battery can fail without warning.

 

[alohart]

<duplicate post>

 

[Bawareca]

The 20ah battery is underspec'd and of questionable quality

Of questionable quality, maybe. Maybe that explains your repeated 12 V battery failure.

Underspec'd, almost certainly not. Since driving with a voltmeter in the center auxiliary power port, I've noticed that the DC-DC charger is almost always charging the 12 V battery, not only when driving, in effect adding the capacity of the Li-ion battery pack to the 12 V system. But unlike in an ICE vehicle, there's no slow starter motor to indicate that the 12 V battery is failing, so i3's 12 V battery can fail without warning.

The 12v battery is good enough when everything is working Ok. It is not enough when for some reason there is no power coming from the HV battery, and this is also when the 12v battery dies. Not under normal circumstances, but when it is exposed to a deep discharge.

 

[Mito]

Having a battery that works ok during " normal circumstances " is all well and good but the test of a well designed system is how it copes with circumstances outside normal parameters and as we can all see the batteries regularly fail when this is the case hence this is why the small battery system is not fit for purpose.
The battery is so small that any degradation of its performance easily pushes it below its level to adequately perform that would not have happened on a larger battery. This is coupled to the fact that the car needs the small battery to run its systems and when it fails the car breaks down completely unlike a combustion car which you could possibly bump start for instance.

 

[EVMan]

So i get it that the original battery is/was 20ah.
My 2016 Rex with Value pack , says something like -larger capacity 12V battery on the sticker
So i guess , now they increased the power of the battery ? Any idea, Whats the larger size OEM installed battery now ?
2017 does not anything on sticker...

For reference the Model 3 has 45Ah. I am sure there are more electronics and OTA will need more power..

 

[jadnashuanh]

FWIW, www.realoem.com shows a 20A AGM battery for ALL of the i3's up through to include the i3s built in February 2018.

 

[Benagami]

My battery will need to be replaced within the next 6 months if not sooner. Has anyone found a 40 ah that will fit?

 

[TOEd]

Original battery is 8"x3 .5"x6.5".

I can't check our i3's battery now because I'm half way around the world. I recall that as it's installed in our i3, the positive terminal is on the right (i.e., on the driver's side for a LHD i3). But I can't recall whether the positive terminal is in the front or back right corner of the battery which can matter when purchasing a replacement battery. With the positive terminal on the right, is it in the front or rear right corner?

On left hand drive (North America) 2015 i3 battery terminals face front of car. Positive terminal is on driver's side (left side of vehicle) and negative terminal is on passenger side (right side of vehicle). Battery is located on passenger side of vehicle immediately behind frunk.

 

[alohart]

My battery will need to be replaced within the next 6 months if not sooner. Has anyone found a 40 ah that will fit?

The battery tray and hold-down won't accommodate a battery that's much larger than the 20 Ah standard battery. BMW does sell a 40 Ah battery that realoem.com lists as an i3 warranty replacement battery, but one owner has reported that fitting this battery required relocating the windshield washer fluid container and modifying the battery tray and hold-down.

The service manager at our local BMW dealer told me that the i3 can use such a low-capacity 12 V battery because the DC-DC converter connects the Li-ion battery pack to the 12 V system to charge the 12 V battery very aggressively which greatly increases the effective capacity of the 12 V battery. One situation in which this does not happen is when an i3 is parked and not being charged. If an i3 is parked for a month or more, the 12 V battery could be discharged to a point that the car's controllers won't boot (and thus the car can't be driven).

 

[EVBob]

Would the properties of a 12v 20ah Lithium Vehicle Battery be substantially better than the AGM for this application? Example:
https://www.lithiumion-batteries.com/products/12v-20ah-lithium-ion-battery/

The 35ah variant of the above is just .5" too wide to fit?.....

 

[alohart]

Would the properties of a 12v 20ah Lithium Vehicle Battery be substantially better than the AGM for this application? Example:
https://www.lithiumion-batteries.com/products/12v-20ah-lithium-ion-battery/

Interesting option. Unlike with older cars, the i3 has a 12 V battery management system that needs to know the properties of a replacement battery so that it can manage it optimally. BMW describes this as "registering" the new battery which seems similar to setting various parameters as is done during coding. We would need to know whether a Li-ion 12 V battery could be properly registered so that the charging system would work optimally. It's likely that BMW didn't design its charging system to work optimally with a Li-ion 12 V battery, but maybe this battery's own internal management system makes it appear similar to a lead-acid battery.

The 35ah variant of the above is just .5" too wide to fit?.....

You could measure the battery box to determine whether it would fit. The cost of the 35 Ah version is quite high considering that an i3 is designed to work with a 20 Ah battery.

Another problem would be the terminals on this Li-ion battery. The orientation appears to be correct, but It doesn't have automotive terminals. I couldn't find a description of the thread size of its screw terminals to determine whether automotive terminals could be installed. When I first installed an AGM battery with screw terminals in our 2000 Honda Insight, I sawed the lead terminals off the original battery, drilled a mounting hole through each of them, and used metric stainless steel bolts to attach these terminals to the battery. This seemed to work fine. Eventually, I replaced this battery with one that had bolt-on automotive terminals as an option.

 

[EVMan]

So in my 2017, if i do not drive it for 4-5 days, (even with battery capacity 50%) , i get a message something like

Independent ventilation systems deactivated , as the vehicle not used for extended period of time.

While i understand this message , when the battery capacity drops below 10% , i do not understand the meaning and purpose of this , when main battery is say above 40%

Like the main battery still has lot of charge
Does the ventilation systems draw power from 12 Volt battery , and its trying to reduce the 12 volt consumption ?
As stated above the DC-DC systems should be able to step in, at this point.

 

[EVMan]

As i mentioned , the 2016 Rex Value package says on the sticker, 5th bullet , that the car has
"high capacity 12 volt battery supply"

While i did not open to check , may be BMW increased the capacity from later 2016 newer models , as they received complaints of parked cars dying. My be it was a Rex Value package thing.

Can i check without opening the frunk ?

For a 20AH battery , they should not be putting this on sticker in 2016 year.

 

[alohart]

So in my 2017, if i do not drive it for 4-5 days, (even with battery capacity 50%) , i get a message something like

Independent ventilation systems deactivated , as the vehicle not used for extended period of time.

I've driven our BEV only 6k miles since November, 2014, so there have been many long parking periods, yet I have never seen that message which seems like another poor translation from German. I don't know what an "independent ventilation system" would be.

Like the main battery still has lot of charge
Does the ventilation systems draw power from 12 Volt battery , and its trying to reduce the 12 volt consumption ?
As stated above the DC-DC systems should be able to step in, at this point.

The A/C compressor is powered by the high-voltage system while the ventilation fan is driven by a 12 V motor. If the ventilation system is on, so should be the DC-DC converter which would charge the 12 V battery.

 

[alohart]

As i mentioned , the 2016 Rex Value package says on the sticker, 5th bullet , that the car has
"high capacity 12 volt battery supply"

While i did not open to check , may be BMW increased the capacity from later 2016 newer models , as they received complaints of parked cars dying. My be it was a Rex Value package thing.

Our 2014 BEV includes option "570 Stronger Electricity Supply". Others have surmised that all i3's have this option which in an ICE BMW would be a higher capacity alternator. In an i3, it might be the DC-DC converter that in effect makes the 12 V battery's capacity equal to that of the large-capacity high-voltage battery pack. I have never read of an i3 with anything but the 12 V 20 Ah AGM battery.

Can i check without opening the frunk ?

No, but even opening the frunk and the passenger-side cover does not expose the 12 V battery very well. You'd need to remove the frunk box to get a better view. There are only 6 Allen screws that attach the frunk box, so removing it is easy.

 

[jadnashuanh]

All of the electronics that aren't directly related to the high voltage system's operation are run off of the 12vdc system: the mirror motors, the wipers, fan, horn, displays, lights, stereo, etc. The main reason why it can get by with a small battery is that it does not need it to start the ICE in the REx, and obviously the electric motor doesn't have a 'starter'. IOW, the load on the thing is fairly small, and consistent, not a high peak draw like on a conventional ICE, especially when it's cold outside.

What sometimes happens with BMW vehicles is one or more of the control modules may not receive the 'shutdown' message from the main computer when you shut the car off. As a result, the static draw on the battery can end up much higher than the design parameters. I know on my other BMW that, if it is not started for a long time, it will gradually shut down some components to help make the 12vdc battery last longer. I wouldn't be surprised if that also happens in the i3. On my ICE, eventually, it will forget some of the stored profile settings (they can be restored with a USB stick if you've saved it). I've not noticed that on my i3 since it gets driven regularly.

I haven't looked at the programming for the i3's 12vdc battery, but on my ICE, the parameters do not include the option for a LiOn battery...only a traditional wet-cell lead acid and an AGM battery. On that one, it also offers a range of CCA values. That, along with resetting the battery age counter, are required for the charging system to be able to manage the battery properly.

Providing the proper max voltage value for the battery, and having the proper charging profile, will go a long ways towards maximizing the life of the attached 12vdc battery. If it doesn't know the type, it could be an issue. There are some LiOn batteries optimized for aircraft use, one of those MIGHT work, as, some of them have internal circuit boards to help mimic a lead-acid one.

Personally, I don't think a LiOn is a good replacement for a typical EV's 12vdc lead-acid battery, but there are some out there that could probably work.

 

[EVBob]

The service manager at our local BMW dealer told me that the i3 can use such a low-capacity 12 V battery because the DC-DC converter connects the Li-ion battery pack to the 12 V system to charge the 12 V battery very aggressively which greatly increases the effective capacity of the 12 V battery. One situation in which this does not happen is when an i3 is parked and not being charged. If an i3 is parked for a month or more, the 12 V battery could be discharged to a point that the car's controllers won't boot (and thus the car can't be driven).

So then if someone is away from their i3 for a while, they could activate climate control via iremote to start up the AC/heater which should activate the dc-dc converter, charging the 12v battery for the 15 minutes climate control is on? If so, then a quick work around for this particular situation would be to set weekly(?) reminders on ones phone to perform this task? Or if parked in a spot where it can be left plugged in, set the precondition to run once a week?

 

[alohart]

So then if someone is away from their i3 for a while, they could activate climate control via iremote to start up the AC/heater which should activate the dc-dc converter, charging the 12v battery for the 15 minutes climate control is on? If so, then a quick work around for this particular situation would be to set weekly(?) reminders on ones phone to perform this task? Or if parked in a spot where it can be left plugged in, set the precondition to run once a week?

That should work, but the battery pack would be discharged with each cabin preconditioning session unless an EVSE is plugged into the charging port. BMW doesn't recommend periodic cabin preconditioning to charge the 12 V battery. Maybe an i3 automatically turns on its DC-DC converter periodically when parked for an extensive period. That would seem to be an easy feature for BMW to have programmed, but I've never heard anyone describe such a feature. The fact that BMW recommends that an i3 be left plugged into an EVSE when parked for an extensive period suggests that this might in fact occur. Otherwise, being plugged into an EVSE turns on the DC-DC converter only while charging is occurring which would be for only the first few hours of being parked. The remainder of the time, the 12 V battery would continue discharging just as it would when not plugged into an EVSE.

 

[EVMan]

So then if someone is away from their i3 for a while, they could activate climate control via iremote to start up the AC/heater which should activate the dc-dc converter, charging the 12v battery for the 15 minutes climate control is on? If so, then a quick work around for this particular situation would be to set weekly(?) reminders on ones phone to perform this task? Or if parked in a spot where it can be left plugged in, set the precondition to run once a week?

Thanks for this tip.!