12v Battery Upgrade?

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ChrisColorado

New member
Joined
Dec 15, 2017
Messages
2
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/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B00T37R8BA&pd_rd_wg=rNvKH&pd_rd_r=99XRV6X9F0F2EF6CQRBR&pd_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
 
ChrisColorado said:
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?
 
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.
 
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).
 
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.
 
jadnashuanh said:
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 ?
 
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.
 
EVMan said:
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.
 
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.
 
graememwl said:
Great info, thanks for sharing. My favorite part is the explicit instruction to "Store the shackle lock key in a safe place." In bold font for emphasis :lol:
I never lock the high-voltage disconnect in the Off position because I am the only person working on our i3 and I know when this disconnect is in the Off position.

That entire site has the best i3 maintenance and repair info that I have found.
 
Hatzenbach said:
where can i get a get a replacement 12V battery without paying BMW prices?

FWIW, on my other BMW, after looking all around, I found that BMW's price was actually cheaper (for the part, not install) than anywhere else I could find. A new battery needs to be 'registered' in the car for it to work best and longest. Other places than the dealer can do that. Where I live, Pep Boys can do it for $35, and if you have the BimmerCode app, you can probably do it yourself.
 
jadnashuanh said:
FWIW, on my other BMW, after looking all around, I found that BMW's price was actually cheaper (for the part, not install) than anywhere else I could find.
Same story for me, especially if you have the CCA discount :)
 
theothertom said:
jadnashuanh said:
FWIW, on my other BMW, after looking all around, I found that BMW's price was actually cheaper (for the part, not install) than anywhere else I could find.
Same story for me, especially if you have the CCA discount :)

Happened to me too :D
 
When it says to disconnect the HV battery is that only for safety reasons or does it have something to do with protecting the computers?
 
flyboy320 said:
When it says to disconnect the HV battery is that only for safety reasons or does it have something to do with protecting the computers?
There is no exposure to high-voltage when changing the 12 V battery, so it's not a safety issue. However, if the high-voltage system is active when the 12 V battery is disconnected, the high-voltage system would suffer an unexpected shutdown which could cause problems. Opening the high-voltage disconnect after the high-voltage system has shut down automatically would prevent potential problems. This step is easy to do, so why take a chance?
 
alohart said:
There is no exposure to high-voltage when changing the 12 V battery, so it's not a safety issue. However, if the high-voltage system is active when the 12 V battery is disconnected, the high-voltage system would suffer an unexpected shutdown which could cause problems. Opening the high-voltage disconnect after the high-voltage system has shut down automatically would prevent potential problems. This step is easy to do, so why take a chance?

OK, makes sense thanks for clarifying.
 
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