Mito
Posts: 27
Joined: Sun Apr 09, 2017 11:55 pm

Re: BMW i3 auxiliary battery sizes

Thu May 18, 2017 2:04 pm

Bawareca wrote:
jadnashuanh wrote: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 :o 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
Posts: 1198
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Fri May 19, 2017 12:42 am

Mito wrote: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.
Aloha,
Art

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

alohart
Posts: 1198
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Fri May 19, 2017 2:14 am

<duplicate post>
Last edited by alohart on Mon Nov 06, 2017 3:17 pm, edited 2 times in total.
Aloha,
Art

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

Bawareca
Posts: 48
Joined: Wed Apr 12, 2017 6:40 pm

Re: BMW i3 auxiliary battery sizes

Mon May 22, 2017 8:17 am

alohart wrote:
Mito wrote: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
Posts: 27
Joined: Sun Apr 09, 2017 11:55 pm

Re: BMW i3 auxiliary battery sizes

Tue May 23, 2017 12:05 am

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
Posts: 137
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: BMW i3 auxiliary battery sizes

Tue Mar 13, 2018 9:55 pm

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..
2016 22KWH Rex.
2017 33KWH Rex

jadnashuanh
Posts: 3841
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: BMW i3 auxiliary battery sizes

Wed Mar 14, 2018 7:27 pm

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.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

Benagami
Posts: 28
Joined: Thu Oct 19, 2017 5:21 am
Location: USA

Re: BMW i3 auxiliary battery sizes

Thu Mar 15, 2018 5:42 am

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
Posts: 87
Joined: Sat Mar 05, 2016 5:15 am
Location: Toronto Ontario Canada

Re: BMW i3 auxiliary battery sizes

Thu Mar 15, 2018 9:44 am

alohart wrote:
Bawareca wrote: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
Posts: 1198
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu Mar 15, 2018 2:45 pm

Benagami wrote: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).
Aloha,
Art

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

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