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

Re: BMW i3 auxiliary battery sizes

Sat Apr 29, 2017 7:53 am

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.

bwilson4web
Posts: 702
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: BMW i3 auxiliary battery sizes

Sat Apr 29, 2017 10:09 am

Bawareca wrote:. . .
My car has no warranty and i have no desire to buy $170+ battery multiple times and . . .
What are the dimensions of the original battery?

I replaced my Prius battery with an Odyssey and never looked back. In my case, I had to use some 1"x1" shims to make sure it was held correctly. Regardless, I was pleased with the results. They make a full line that includes popular motorcycle batteries.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

jadnashuanh
Posts: 4483
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: BMW i3 auxiliary battery sizes

Sat Apr 29, 2017 6:59 pm

If your OEM 12vdc battery dies, it is either really old, or you have something wrong with the car, and a larger battery may not resolve that issue. Pretty much all modern cars expect you to drive them periodically. If you don't, it can discharge the battery. My GT has a HUGE battery, only gets driven every few months or so. If I don't put it on a battery maintainer, it will discharge that battery. Makes the one in the i3 look like a flashlight battery.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

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

Re: BMW i3 auxiliary battery sizes

Wed May 03, 2017 2:55 pm

bwilson4web wrote: What are the dimensions of the original battery?

I replaced my Prius battery with an Odyssey and never looked back. In my case, I had to use some 1"x1" shims to make sure it was held correctly. Regardless, I was pleased with the results. They make a full line that includes popular motorcycle batteries.

Bob Wilson
Original battery is 8"x3 .5"x6.5".
Last edited by Bawareca on Thu May 04, 2017 5:52 am, edited 1 time in total.

alohart
Posts: 1674
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu May 04, 2017 12:37 am

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?
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

Thu May 04, 2017 5:52 am

alohart wrote: 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?
Both terminals are at the front. Positive is on the passenger side, negative on the driver side (LHD).

alohart
Posts: 1674
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu May 04, 2017 6:42 am

Bawareca wrote:Both terminals are at the front. Positive is on the passenger side, negative on the driver side (LHD).
Hmm, I disconnect and reconnect the negative terminal every year when we store our 2014 BEV. Maybe my memory is failing me, but I could have sworn that the negative terminal is on the passenger side (LHD). Realoem shows that it is, at least on a 2014 BEV built in August, 2014. Maybe i3's built later have a different battery configuration. Realoem does confirm that the battery terminals are at the front of the battery as you stated.
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

Thu May 04, 2017 12:36 pm

I dont have the car in front of me. I may be mistaken because of the power distribution box which is on the passenger side.

alohart
Posts: 1674
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: BMW i3 auxiliary battery sizes

Thu May 04, 2017 1:26 pm

A Mazda Miata AGM battery might fit (7 ¾"L x 5 ⅛"W x 7 ¼"H), but its capacity (25Ah) and weight are needlessly high.

An Odyssey PC680 AGM battery might also fit (7.9"L x 3.8"W x 7.8"H). If so, this is the battery I'll probably buy when I need to replace our current battery. Its capacity is 16Ah which is a little less than our i3's original 20Ah battery which should not be a problem. A set of brass automotive terminals would be needed as well.
Aloha,
Art

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

bwilson4web
Posts: 702
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: BMW i3 auxiliary battery sizes

Thu May 04, 2017 6:26 pm

Bawareca wrote:
bwilson4web wrote: What are the dimensions of the original battery?
. . .
Original battery is 8"x3 .5"x6.5".
Ok,

I found three Odyssey battery candidates:
  • PC370 - 15Ahr - 7.9"x3.0"x5.5"
  • PC545 - 13Ahr - 7.01"x3.38"x5.16"
  • PC680 - 16Ahr - 7.25"x3.11"x7.55" , but 1" too tall
Some assembly is required which means inspecting the mounting location and using shims to make sure it is secure. You don't want ordinary road vibration to 'wear a hole' in the case. Also, short, jumpers may be needed to connect to the existing electrical connectors.

Finally, we want to monitor the 12V voltage through a couple of power cycles to make sure there are no surge loads that drop the voltage below 11.95V. For example, the Prius has a hydraulic accumulator pump that powers the brakes and there are other accessories that put a brief but significant load on the 12V battery:
  • PC370 - 200 CCA - 425 PHCA (5 sec) - 15Ahr - ~$200
  • PC545 - 150 CCA - 460 PHCA (5 sec) - 13Ahr - ~$100
  • PC680 - 170 CCA - 520 PHCA (5 sec) - 16Ahr - ~$100
The easiest answer is the PC545, low cost and smallest size but also lowest capacity. PC680 would be the next IF there is enough head room. PC370 is strong and fits but expensive, nearly twice the price. But how good does the battery have to be?

I'll take a look this weekend at instrumenting the battery that was replaced in December. I can use a shunt resistor on the ground and B+ resistor network feeding an Arduino.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

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