ChrisColorado
Posts: 2
Joined: Fri Dec 15, 2017 8:12 pm

12v Battery Upgrade?

Thu Jan 18, 2018 8:33 am

My battery will be over three years old shortly and I'd rather replace it early than be stranded on day--Especially with our cold mountain winters.
Does anyone know if this battery will work?

It's made as a replacement battery for a motorcycle, so I imagine it's more sturdy and less sensitive to charging variations.

The original battery is 8"x3 .5"x6.5" and this one is 6.49” x 3.38” x 5.11”---a touch smaller in every dimension while having almost 50% more capacity at 35AH compared to the original 24AH battery.

Battery Tender Lithium Iron Phosphate 12V 35AH Battery
https://www.amazon.com/dp/B00T37R8BA/re ... rd_w=pw6aB
Quad terminal configuration and the ability to be mounted in any direction makes installation a snap; Case Dimensions: 6.49 inch (165 millimeter) length x 3.38 inch (86 millimeter) width x 5.11 inch (130 millimeter) height; Weight: 3.75 pounds

Thank you.

Chris

alohart
Posts: 2121
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 12v Battery Upgrade?

Thu Jan 18, 2018 2:11 pm

ChrisColorado wrote:Does anyone know if this battery will work?

It's made as a replacement battery for a motorcycle, so I imagine it's more sturdy and less sensitive to charging variations.

The original battery is 8"x3 .5"x6.5" and this one is 6.49” x 3.38” x 5.11”---a touch smaller in every dimension while having almost 50% more capacity at 35AH compared to the original 24AH battery.
To be clear, the capacity rating is 96 Wh which is 8 Ah (= 96 Wh / 12 V). The original i3 battery is 20 Ah. The battery manufacturer claims that this battery can replace a lead-acid battery whose capacity is from 26-35 Ah. I'm guessing that because the voltage of a LiFePO4 battery varies much less over its charge level range compared with a lead-acid battery, it is able to provide more power within an acceptable voltage range compared with a lead-acid battery. Its capacity would likely be sufficient for an i3 because an i3 turns on its DC-DC converter very aggressively essentially increasing the 12 V capacity to that of its large Li-ion battery pack. I think a LiFePO4 battery is more susceptible to being permanently damaged by being discharged completely, so this would be a risk.

Unfortunately, when the 12 V battery of a BMW is replaced, information about the battery is supposed to be registered with the car's 12 V battery management system so that it maintains the battery appropriately. This information might also used by the 12 V battery management system to determine when the battery is failing. I doubt that the unique characteristics of a 12 V LiFePO4 battery are supported by this 12 V battery management system. This could make any DIY 12 V battery replacement problematic, maybe even more so with a 12 V LiFePO4 battery. Never having owned a car with such a requirement, could someone explain the consequences?
Aloha,
Art

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

jadnashuanh
Posts: 5034
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 12v Battery Upgrade?

Thu Jan 18, 2018 4:56 pm

Maybe this will help as I just recently replaced the battery in my GT.

The computer information that needs to be programmed includes the following (and, I'm guessing, it's the same in the i3):
- the capacity of the battery
- when it is installed (it appears to be an upcounter, so essentially, you reset it)
- the type of battery (it only showed wet lead-acid (conventional), and AGM types)

It's my understanding that it takes into account how old the battery is to determine how aggressively it can charge the battery and the actual charging voltage to best accommodate the type of the battery. In the case of the GT, there is a clutch on the alternator, and knowing the battery characteristics will help to determine when it actually turns on charging as opposed to more 'normal' cars that only rely on the battery voltage to alter the charging, and essentially are constantly holding it as close to full as possible. The advantage of an AGM type is that they are less likely to be damaged by a deeper discharge, so you can pick and choose when you want to charge it based on the current situation. In my GT, it normally only charges the battery when it is first started, but then later, only when you let off on the accelerator and then stops that process once you've stopped the car and are idling. That slight load can help decelerate the car, but can get twitchy unless they remove it just prior to you stopping so that last bit is smoother.

A Lithium based battery will have very different charge status logic than the types (I think) the car understands, so it probably would not last as long.

I've not looked in the area to estimate how easy it may be to find an alternate battery for the i3. Because BMW does appear to list a larger, alternate battery, it appears that it can be made to fit. They may actually have a different clamp or tray to accommodate that larger battery...just don't know. Others have indicated it doesn't fit without mods, but can't confirm.

Personally, I'd want an AGM battery in there. If you can find a larger one, that may be useful, but larger also means heavier and (maybe) more costly.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

i3daytonoh
Posts: 24
Joined: Thu Jan 18, 2018 8:19 pm
Location: Dayton, OH

Re: 12v Battery Upgrade?

Thu Jan 18, 2018 8:53 pm

I have one of these Battery Tender batteries installed in my scooter for the past two years and it works really well. However, I would not recommend it for the i3. I do not think the battery cable connectors will be compatible. Also, these batteries are not tolerant of being over charged which can lead to catastrophic failure (fire). The instructions with the battery warn not to charge when the temperature is below 14 degrees F (-10C).
2014 Andesite Silver Giga BEV

jadnashuanh
Posts: 5034
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 12v Battery Upgrade?

Thu Jan 18, 2018 8:58 pm

Some BMW documents someone posted say use of a battery tender on an i3's installed battery can cause equipment malfunctions...IOW, don't do it. If the car is going to be left for extended periods unused and you cannot plug in an EVSE, it's probably best to remove the 12vdc battery and then, you can put it on a tender. Note, not all tenders understand AGM batteries, and could damage them. You want one that does have an AGM setting on it.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

ChrisColorado
Posts: 2
Joined: Fri Dec 15, 2017 8:12 pm

Re: 12v Battery Upgrade?

Sat Jan 20, 2018 3:12 pm

Thanks to everyone for time and effort. I learned a lot and you'll stopped me from making a mistake.
Thank you.

EVMan
Posts: 314
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: 12v Battery Upgrade?

Wed May 02, 2018 4:28 pm

jadnashuanh wrote:Some BMW documents someone posted say use of a battery tender on an i3's installed battery can cause equipment malfunctions...IOW, don't do it. If the car is going to be left for extended periods unused and you cannot plug in an EVSE, it's probably best to remove the 12vdc battery and then, you can put it on a tender. Note, not all tenders understand AGM batteries, and could damage them. You want one that does have an AGM setting on it.
For my knowledge , is it ok to disconnect this battery for some time and then reconnect it ?
Will the car just boot up again, or will it need any special re configuration or a dealer visit ?
2017 33KWH Rex
Model 3 Long Range
Solar ToU Plan

jadnashuanh
Posts: 5034
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 12v Battery Upgrade?

Wed May 02, 2018 6:41 pm

I don't know, but my guess is it probably would be okay. Suggest you run that by the dealership. I don't think it would be any different than the battery going flat on its own.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

alohart
Posts: 2121
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 12v Battery Upgrade?

Wed May 02, 2018 7:14 pm

EVMan wrote:For my knowledge , is it ok to disconnect this battery for some time and then reconnect it ?
Will the car just boot up again, or will it need any special re configuration or a dealer visit ?
For 3 periods of 6-9 months, we stored our 2014 BEV. I left the Li-ion battery pack's charge level at ~50% and disconnected the 12 V battery so that it would not be discharged fully and thus ruined.

However, there is a special procedure for disconnecting and reconnecting the negative cable of the 12 V battery that involves deactivating the high-voltage system.

Because some stored information is lost when the 12 V battery is disconnected, it's best to back up driver profiles to a USB flash drive so that it can be restored after the 12 V battery is reconnected. Even though I did this, I had to do a few things like setting the clock after reconnecting the 12 V battery, but no special configuration or dealer visit was necessary. Our car started normally.
Aloha,
Art

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

Kiwi
Posts: 80
Joined: Sun Feb 15, 2015 9:45 pm
Location: Auckland

Re: 12v Battery Upgrade?

Wed May 02, 2018 11:43 pm

Doesn't BMW USA have 5 years warranty which includes free recovery for flat batteries or keys locked in the car. It even allows the cost of accommodation if required.

Return to “News and Main BMW i3 Forum Discussions”