12V (AUX 18L) new battery voltage shows 11.9V

[alohart]

That's a great knowledge on the charging mechanism on i3. I'm sure that other i3 owners would be pleased to know that they can skip the overpriced OEM battery with ancient tech to LFP with no problem on charging.

I would caution any i3 owner living in a climate with cold winter weather not to buy a LFP battery that doesn't include an automatic cell heater. The Ohmmu battery that would fit an i3 and would definitely have a cell heater, the LFP battery for a Rivian truck, is considerably more expensive than the OEM battery or the G1DC22-B deep cycle LFP battery that you are considering and that doesn't claim to include an automatic cell heater.

You are right on LFP voltage output curve, it is quite flat throughout the capacity range, so traditional charger should see it as close to full when LFP is at 50% or more in capacity.

My CTEK battery charger that doesn't include a LFP setting isn't confused by the higher voltage of my Ohmmu LFP battery. According to the Ohmmu smartphone app, my charger charges the battery to 100%.

 

[neversummer]

I would caution any i3 owner living in a climate with cold winter weather not to buy a LFP battery that doesn't include an automatic cell heater. The Ohmmu battery that would fit an i3 and would definitely have a cell heater, the LFP battery for a Rivian truck, is considerably more expensive than the OEM battery or the G1DC22-B deep cycle LFP battery that you are considering and that doesn't claim to include an automatic cell heater.

My CTEK battery charger that doesn't include a LFP setting isn't confused by the higher voltage of my Ohmmu LFP battery. According to the Ohmmu smartphone app, my charger charges the battery to 100%.

I just replaced my wife's i3 12v battery this afternoon, and I can see it could tricky to install OEM battery terminal on Ohmmu.

I think I should get Ohmmu's Rivian battery since I don't know where my car will end up if I decide to get a different EV in the future. At least next owner won't have to worry about using the car in cold weather.

Thank you so much!

 

[Dutchi3]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

 

[alohart]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

I am concerned about that after I noticed that our LFP 12V battery is almost always near a 100% charge level in our i3. I am not aware of any charge level buffers in this LFP battery. Fully charging an LFP battery cell is recommended, but it is not recommended to allow it to remain fully charged for long periods. For its longest life, battery cell experts recommend storing a LFP battery cell at a 50% charge level just like other lithium chemistries.

I will try disabling the charging of our LFP battery until its charge level decreases below 50%. I can disable charging using the Ohmmu smartphone app that communicates with the battery's BMS via Bluetooth. I can also monitor the 12V battery's charge level with the Ohmmu app, so with a little effort, I could probably keep the average charge level near 50%. The voltage at 40% is 13.1V which is higher than the full charge voltage of the OEM battery, so the car wouldn't notice that the 12V battery's charge level is 40%. I would have to learn how fast it discharges while parked so that the 12V battery's charge level doesn't decrease too low.

However, I have a spare LFP battery, so if managing the charge level of the LFP battery is too onerous, I could just ignore its charge level and replace it with my spare LFP battery when it fails.

 

[BattlePenguin]

I just replaced my wife's i3 12v battery this afternoon, and I can see it could tricky to install OEM battery terminal on Ohmmu.

I think I should get Ohmmu's Rivian battery since I don't know where my car will end up if I decide to get a different EV in the future. At least next owner won't have to worry about using the car in cold weather.

Thank you so much!

Did you have to register the battery with the car? I don't have the equipment to do the registration, so I was thinking about asking paying BMW to do it, but they want $300 for the installation. Did you install your battery by yourself and skip registration? If you did not skip registration, what tool did you use to register the batter? Maybe the procedure is called by other names, but the person at BMW told me that you have to do that step in order for the car to take full advantage of the battery or the battery to get full power... something like that

 

[neversummer]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

Did you have to register the battery with the car? I don't have the equipment to do the registration, so I was thinking about asking paying BMW to do it, but they want $300 for the installation. Did you install your battery by yourself and skip registration? If you did not skip registration, what tool did you use to register the batter? Maybe the procedure is called by other names, but the person at BMW told me that you have to do that step in order for the car to take full advantage of the battery or the battery to get full power... something like that

I replaced the battery myself, but I bought the battery from local BMW dealer. My local BMW dealer also wanted about $300, $299 to be exact, and claimed that it's that price b/c they have to register the battery. Registration is needed only if you install different size battery, but since I bought OEM, the setting is the same. I did use BimmerCode, you can buy from App store, with Bluetooth ODBC reader to double check original setting to see if it was set at 20AH.

The procedure was straight forward, just pure mechanical labor, nothing to reprogram and not even setting the clock. It will show incorrect time once new battery is installed, but it will automatically sync the time with GPS once your car has clear view of the sky.

 

[alohart]

Registration is needed only if you install different size battery, but since I bought OEM, the setting is the same. I did use BimmerCode, you can buy from App store, with Bluetooth ODBC reader to double check original setting to see if it was set at 20AH.

BimmerCode can change the battery capacity or type from the default OEM 20 Ah AGM battery, but BimmerLink is required to register a replacement battery. Registration records the date and maybe mileage when the battery was replaced so that a mechanic would know in the future when the battery had been replaced.

There's no evidence that registration affects 12V battery charging on an i3 as it does on BMW vehicles with alternators, so I wouldn't pay a mechanic to register a replacement battery. For what a mechanic would charge, one could license BimmerLink and buy an OBD to WiFi or Bluetooth adapter to register the battery oneself.

 

[neversummer]

BimmerCode can change the battery capacity or type from the default OEM 20 Ah AGM battery, but BimmerLink is required to register a replacement battery. Registration records the date and maybe mileage when the battery was replaced so that a mechanic would know in the future when the battery had been replaced.

There's no evidence that registration affects 12V battery charging on an i3 as it does on BMW vehicles with alternators, so I wouldn't pay a mechanic to register a replacement battery. For what a mechanic would charge, one could license BimmerLink and buy an OBD to WiFi or Bluetooth adapter to register the battery oneself.

Thank you for the correction

 

[BattlePenguin]

Ok, I think I'm all set. I'll let you know how it goes.

 

[JoeCool88]

As I've seen on my 2018 94Ah i3, the 12V battery has an of course essential, but on the other hand very limited role to play in the cars electric architecture. This role is to supply enough energy to fullfill the commands from the remote control, e. g. to unlock it when the car is stationed/locked. But as soon as you press the starter button w/o breaking, or start a function like e. g. the pre-heating or pre-AC remotely, the DC-DC converter jumps in and supplies 14 V to the car, thus charging the 12V battery. And even after switching down and closing the i3, the 14 V supply remains active for a few minutes.
Taking into consideration the short period of time and relatively low current when needed, as well as a certain self-discharging when not engaged and the battery's weight, BMW dimensioned it not bad imho.
In aviation industry the policy is to replace some items i. a. w. their mean time between failure (MTBF). If experience shows that, due to the operational constraints and climate conditions, a battery 'dies' after 5-6 years (= MTBF), in aviation they would replace it after 3 years. I would suggest to replace the i3 12V battery systematically after 4 years.
At a price for a standard battery (like the AUX18L20Ah, TX24HL or YTX24HL-BS) of approx. 100 to 150 Euro/USD, this means 25 to 37 Euro per year. The local BMW dealer will charge you that for opening his door. But highly likely you will never ever face any 12V battery issues on your i3.
This might be ancient tech, but keeps the type certificate of the car valid. And might safe you from the one or other uncomfortable question from your insurance, in case of an even small electrical fire on the car, which occured for which reason ever ;o).