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

[i3Houston]

All,
The OEM batter was over 56 months old. Cig. lighter adapter car volt meter [Amazon link ] showed 11.8volt. Clearly it was time to replace. So after fully charging Remy AUX 18L and verifying with volt meter that battery is producing 12.9V, battery was then installed in the car.

With the new battery in, i3 turned on and drove normally. Only prompt was to set the time (date was retained somehow). But, the voltage meter in the cigarette lighter adapter (front, center, under console) is still showing 11.8V. What could be causing this?

The 56 months old battery on testing with volt meter shows 12.9V as if its new but I think voltage under no load can be higher.

 

[EvanstonI3]

I would try some other way to measure the voltage than with a cheap cig lighter adapter volt meter then. Maybe just get a different one. The one you have could be bad. I have one plugged in just for reference and when the car is ON and ready to drive it shows 14.4-14.9 volts. Also try plugging into the port under the armrest instead to see if there is any difference. That's where mine is.

 

[mojo]

It would be a bit unusual, but perhaps BMW regulate the 12V outlets to be no more than 12V? TBH I've never checked the exact voltage at mine.

Was the 11.8V at rest and powered down, or with the car in "drive ready" state? My car is just over 2 years old, and the battery voltage on that drops to 11.8V if I unlock it and the "leaving home" headlights turn on. It seems that this voltage is just too high to force the car's built-in DC-DC converter to turn on.

But, as EvanstonI3 says, as soon as you put the car into "drive ready" state, the voltage should go up to around 14.4V. I should add that I measure the voltage directly from the battery, with a display in the car that is permanently on. That's probably a more accurate way to do it than via a cig lighter socket voltmeter.

[Edit: I should add that a lead/acid battery should not show more than 12.9V under "steady state" conditions. If yours does, it's probably because it had been on charge a few minutes earlier. If left for 30 minutes without any input or output, it should settle down to its natural resting voltage.]

 

[i3Houston]

It would be a bit unusual, but perhaps BMW regulate the 12V outlets to be no more than 12V? TBH I've never checked the exact voltage at mine.

Was the 11.8V at rest and powered down, or with the car in "drive ready" state? My car is just over 2 years old, and the battery voltage on that drops to 11.8V if I unlock it and the "leaving home" headlights turn on. It seems that this voltage is just too high to force the car's built-in DC-DC converter to turn on.

But, as EvanstonI3 says, as soon as you put the car into "drive ready" state, the voltage should go up to around 14.4V. I should add that I measure the voltage directly from the battery, with a display in the car that is permanently on. That's probably a more accurate way to do it than via a cig lighter socket voltmeter.

[Edit: I should add that a lead/acid battery should not show more than 12.9V under "steady state" conditions. If yours does, it's probably because it had been on charge a few minutes earlier. If left for 30 minutes without any input or output, it should settle down to its natural resting voltage.]

In Drive state voltage jumps to 14.0V with new battery (old battery showed 14.4V).

In rest mode (after unlocking), voltage is showing 11.8V just like yours. So this seems normal.
The cheap cig lighter seems to working though, in my other car it did report the voltage correctly. But I will try another outlet to test the voltage.

 

[EvanstonI3]

Under resting voltage, mine will show 12.4 because there is an accessory draw on the 12v when you unlock and open the doors to activate the power ports. If you measured the voltage at the battery terminals without the car in accessory mode, you would find the voltage to be higher, closer to 12.9. 11.8 still seems really low to me from the power port.

 

[i3Houston]

The resting voltage has climbed up to 12V now. Sometimes it shows 12.2V but then drops to 12V after Dashcam turns on. I was hoping to see 12.5V since Remy battery is new (11/2023) and fully charged.

I wil measure the voltage at the battery terminals when car is in ready state and post an update.


Voltage jumps to 14.0V and (not 14.4V ) when car is put in Ready state. I am wondering if there is need to register the battery via Bimmer link in this situation, thoughts?

 

[EvanstonI3]

Registering the battery does nothing. Nothing. The last 12v I installed where I registered the battery showed a lower voltage when "ON" (maybe 14.2) for awhile and then gradually went up to 14.8 where it is now.

If you are going to measure the voltage of the 12v at the battery terminals, don't do it when the car is ON and in READY state. You should pop the frunk, close the doors, keep the fob away from you and wait about 30 minutes. The accessories will shut off after about 15 minutes, but you should let it sit a bit longer to rest. Then remove the Frunk tray if necessary and measure the voltage at the terminals to see what the voltage is at a resting state.

 

[i3Houston]

ON state voltage at Cig lighter voltmeter - 12.0V. And at terminals of the battery - 12.44V.

In Gas car,
Accessories OFF - 12.55V at battery terminals. Cig lighter is OFF
Accessories ON - 12.42V at battery terminals. Cig lighter shows 12V

Cig lighter appears to be under reporting by 0.5V vs. battery terminal OR other assumption is that both i3 and Gas car are adjusting voltage to 12V at cigarette lighter socket.

 

[EvanstonI3]

When it is "On" there is a draw on the power so the voltage reading will drop. But it SHOULD read the same at the terminals and the cig lighter port. Really looks like the cig lighter volt meter is not functioning properly.

 

[alohart]

When it is "On" there is a draw on the power so the voltage reading will drop. But it SHOULD read the same at the terminals and the cig lighter port. Really looks like the cig lighter volt meter is not functioning properly.

I agree. The 12 V voltmeter I've inserted into the auxiliary power port beneath the center of the dashboard displays almost exactly the same voltage as the 12 V system monitor installed on the battery terminals. Both display 14.2±1 V when the DC-DC converter is on. I've never seen 14.8 V.

 

[i3Houston]

The proper voltmeter measured 12.50V at cigarette outlet when car was in ON state so that shows the new Remy battery is working normally. And the cig. lighter voltmeter adapter that was purchased from Amazon is faulty.

Thank y’all so much for your guidance!

FWIW, Dealership quoted around $350 for battery, $250 for labor, $100 for other work ( total $700, another dealership quoted $750).
DIY replacement - Remy Battery+shipping ($168) [Coupon for 15% is RDBC], 10mm wrenche and 10mm socket wrench extender (~$20). Total $190 and 45 minutes of labor excluding learning time on YT, preparing checklist, buying tools etc.

 

[weajd]

If you are not measuring voltage directly at the terminals of the battery, you should expect lower numbers due to voltage drops under cables and terminals before your voltmeter can measure. You are not likely getting low resistive contact to your battery by using the cigarette lighter port.

Your battery is likely to have a nominal 12 volt value due to the cells in the battery when the car is turned off.
When you turn the car on, a generator, alternator or in the i3 case maybe a voltage regulator, has to provide a few volts more than the nominal in order to charge the battery. It may be 14.4 volts directly at the battery terminals when the car is turned on so that power (current) is being sent back into the battery.

That i3 battery is more like a motorcycle battery because it is just for the accessories when the car is off. If I remember right, the i3 uses the Lithium Ion battery to start up the REX engine, if available, so that "Sealed Lead Acid" battery is used for accessories (e.g., alarm, comms., key lock) when the car is off.

Someone should look into using the frunk space to putting a larger lead acid battery in the i3 to avoid so frequent changes. It would weigh more and reduce range some, but it would eliminate some of the headaches from that small battery. I remember the engine compartment space in my BMW 2002Tii being so small, I moved the battery to the trunk and that improved its reliability.

 

[weajd]

I think the i3's engine microprocessor keeps track of voltage.
An OBD2 reader may be able to read out the voltage being sensed by a sensor closer to the battery.
That is probably a more accurate voltage measurement than what is being read by a voltmeter at the cigarette lighter.

 

[alohart]

If you are not measuring voltage directly at the terminals of the battery, you should expect lower numbers due to voltage drops under cables and terminals before your voltmeter can measure. You are not likely getting low resistive contact to your battery by using the cigarette lighter port.

The magnitude of a voltage drop across a resistance is proportional to the current. There is likely very little current flowing from the battery through the cigarette lighter port fuse to the cigarette lighter port. A voltmeter requires very little power, so I'd be surprised if there's a noticeable voltage drop in this case. The voltmeter in my auxiliary power port displays the same voltage as my 12 V system monitor installed across the battery terminals within 0.1 V.

Your battery is likely to have a nominal 12 volt value due to the cells in the battery when the car is turned off.
When you turn the car on, a generator, alternator or in the i3 case maybe a voltage regulator, has to provide a few volts more than the nominal in order to charge the battery. It may be 14.4 volts directly at the battery terminals when the car is turned on so that power (current) is being sent back into the battery.

The i3 doesn't have a generator or alternator. The 12 V battery is charged by a DC-DC converter that converts high voltage from the HV battery pack to ~14.3 V.

Someone should look into using the frunk space to putting a larger lead acid battery in the i3 to avoid so frequent changes. It would weigh more and reduce range some, but it would eliminate some of the headaches from that small battery.

A better solution might be to replace the original absorbent glass mat (AGM) battery with a lithium iron phosphate (LFP) battery as I have done. Tesla has been installing lithium chemistry 12 V batteries for a few years. This LFP battery weighs about 1/3 that of the AGM battery while having about twice the usable capacity. Its expected lifetime should be considerably greater which should justify its higher cost. This battery is self-heating so it works in cold weather. The battery includes a Bluetooth radio that communicates with a smartphone with the Ohmmu app installed. This app reports total voltage, current in and out, power, charge-discharge cycle count, age, temperature, and the voltage of each of its 4 cells. It supports turning off charging or discharging and updating the battery's firmware. I suspect that more vehicle manufacturers will replace lead chemistry batteries with lithium chemistry 12 V or 48 V batteries.

 

[mojo]

Someone should look into using the frunk space to putting a larger lead acid battery in the i3 to avoid so frequent changes.

As with everything weight-related, it's going to be a compromise. You only have to look at some of the weight-saving efforts that BMW has gone to on this car - such as the covers that sit on either side of the frunk box. They are feather-light. BMW could have put in solid pieces of plastic and that would have only added a few tens of grams extra, but it all adds up.

So yes - you can fit a 20 kilo battery instead of the factory 5-kilo battery, in the same way that you can fit bigger, heavier wheels, and a bigger fuel tank on the REx. It will all make a significant difference on what is essentially a 1200 kilo car.

Others have suggested replacing the lead/acid battery with a small 12V lithium ion battery, and that (to me) makes more sense. In the original design, BMW didn't do that and the reason was almost certainly cost - but LiFePO batteries have become significantly cheaper in recent years.

 

[neversummer]

The magnitude of a voltage drop across a resistance is proportional to the current. There is likely very little current flowing from the battery through the cigarette lighter port fuse to the cigarette lighter port. A voltmeter requires very little power, so I'd be surprised if there's a noticeable voltage drop in this case. The voltmeter in my auxiliary power port displays the same voltage as my 12 V system monitor installed across the battery terminals within 0.1 V.

The i3 doesn't have a generator or alternator. The 12 V battery is charged by a DC-DC converter that converts high voltage from the HV battery pack to ~14.3 V.

A better solution might be to replace the original absorbent glass mat (AGM) battery with a lithium iron phosphate (LFP) battery as I have done. Tesla has been installing lithium chemistry 12 V batteries for a few years. This LFP battery weighs about 1/3 that of the AGM battery while having about twice the usable capacity. Its expected lifetime should be considerably greater which should justify its higher cost. This battery is self-heating so it works in cold weather. The battery includes a Bluetooth radio that communicates with a smartphone with the Ohmmu app installed. This app reports total voltage, current in and out, power, charge-discharge cycle count, age, temperature, and the voltage of each of its 4 cells. It supports turning off charging or discharging and updating the battery's firmware. I suspect that more vehicle manufacturers will replace lead chemistry batteries with lithium chemistry 12 V or 48 V batteries.

Hello, as I was researching on 12V LFP battery for BMW i3, I came across your post. How is your experience with 12V LiFePO4 battery in your BMW i3 so far? Are you using Ohmmu G1DC22-B 22AH model?

Thank you!

 

[alohart]

Hello, as I was researching on 12V LFP battery for BMW i3, I came across your post. How is your experience with 12V LiFePO4 battery in your BMW i3 so far? Are you using Ohmmu G1DC22-B 22AH model?

When I was looking for a LFP battery whose physical size was similar to the OEM battery, I looked through Ohmmu's automotive batteries but not their deep cycle batteries. The batteries for the Rivian truck were the perfect physical size, but I didn't need 2 batteries. I asked Ohmmu about selling me only 1 Rivian battery (at that time, there was no option to buy only 1 as there is now) plus 2 Tesla Model S screw-on brass SAE terminals. Ohmmu told me that they were interested in offering a LFP battery for the i3 but didn't have an i3 to perform a test fitting. They told me that they would sell me a battery for only the shipping cost if I would document the installation in our i3 which I agreed to do.

I was surprised when I received 2 LFP batteries with generic labelling, 2 sets of SAE posts, and 2 ¼" fitting spacers. I discovered that they were ⅜" taller than the OEM battery and ½" taller than the Rivian battery which makes installation more difficult than it would have been for a Rivian battery. Thanks for alerting me of the G1DC22-B whose measurements match those of the batteries I received, so I assume that I have 2 G1DC22-B's rather than Rivian batteries.

The increased LFP battery height meant that I had to move the spacer from the underside of the horizontal section of the battery hold-down bracket to the inside of the vertical section of this bracket so that the top bracket screw would align with its nut. I mounted 1 Ohmmu fitting spacer on the front of the battery with double-sided tape. The relocated spacer plus the Ohmmu spacer allowed the bracket to secure the battery which is ½" less wide than the OEM battery. The shorter length of the LFP battery isn't a problem.

Threading the top bracket screw is still more difficult than with the OEM battery, so I created a thin PET washer from a supermarket strawberry container to secure this screw. I slid this washer onto the top bracket screw from the back side of the bracket which prevents the screw from falling out and disappearing into the void below while trying to thread it into its nut (I was lucky to find this screw when it fell before I made the washer). Because the bracket is higher than with the OEM battery, I added a couple of washers between the bottom of the bracket and the bottom of the battery box.

I initially had problems with the screw-on terminals not making good, solid electrical connections with the battery terminals. Those used with the OEM battery don't fit at all on the LFP battery. The bases of Model S screw-on terminals are too large to fit in the recesses in the battery case around the battery terminals, so I used a Dremel tool to grind a couple of flat areas on the sides of the screw-on terminal bases so that they would fit into these recesses. This has the added benefit of preventing the SAE posts from rotating should their attachment screws loosen.

The undersides of the screw-on terminals are recessed and don't contact the tops of the battery terminals, so I added 2 brass washers to each terminal to fill these gaps and create good, solid electrical connections that don't depend on the stainless steel attachment screws to conduct electricity.

So installing an Ohmmu G1DC22-B battery in an i3 isn't plug-and-play, but it's not too difficult. The Rivian battery would be a better fit but at almost twice the current sale price of the G1DC22-B battery. If you live where ambient temperatures could be cold, the Rivian battery is self-heating so that it would function well in cold weather. There's no such claim for the G1DC22-B battery. This isn't a problem for me in Honolulu, but if you live in a colder climate, ask Ohmmu whether the G1DC22-B battery is self-heating. If not, it might not work well in cold temperatures.

I installed a Ohmmu G1DC22-B battery in our 2019 i3 last November and moved it to our new-to-us 2021 i3 in June. I've had no electrical problems since replacing the OEM battery. The DC-DC converter's 14.0-14.4 output voltage keeps the LFP battery fully charged.

I really like the Ohmmu battery's Bluetooth radio and smartphone app which allow me to monitor the state of the battery (charge level, overall and individual cell voltages, current flow, temperature, cycle count, age, error alerts, and the ability to enable/disable charging and discharging). I could disable discharging so that I wouldn't have to disconnect the battery's negative cable when storing our i3 for several months which I do almost every year. This might also be a security feature that could prevent a thief from starting an i3, but I don't know how an i3 would react to having its 12V power turned off regularly.

I also moved my 12V system logger to our 2021 i3. It shows that the voltage of the Ohmmu battery is typically 0.5V higher than that of the OEM battery and that its voltage doesn't sag nearly as much under load or decrease as much as the battery's charge level decreases. I think that this would prevent many of the diagnostic trouble codes (DTC's) from being stored when the OEM battery fails and its voltage drops too low. Hopefully, the warning signs of the failure of a LFP battery would occur before its output voltage decreases so much that DTC's are stored. I hope that my LFP battery lasts much longer than the typical OEM battery lifetime.

 

[neversummer]

Thank you so much for sharing your installation tips, all the modifications to the battery, and your experience with Ohmmu battery. I live in Southern CA and the weather doesn't get cold that often. I think I want to try one. I just got OEM battery from BMW dealer today for my wife's 19" i3s, and I think mine will need new battery soon too. Therefore, I start looking for alternative b/c OEM 12v is the only thing outdated about this car. I love i3, it's a perfect car for our daily use. I read a lot about BMW i3 dead 12v, so I installed battery pigtail on both cars on the 1st day we got them. I can probably remove the pigtail if I can successfully install Ohmmu in my car.

I was not sure about DC-DC converter charging Ohmmu battery since on the website said Absorption: 14.4 to 14.6 volts. I'm glad to hear that i3 DC-DC has no problem charging it. The physical aspect of the battery fitment sounds difficult too, but at least I can try to modify it following your written guide.

By the way, Ohmmu G1DC22-B is a 22AH battery. Do you have to recode the car after the installation for the extra 2AH capacity over OEM?

 

[alohart]

Thank you so much for sharing your installation tips, all the modifications to the battery, and your experience with Ohmmu battery. I live in Southern CA and the weather doesn't get cold that often. I think I want to try one.

Its sales price makes it very attractive.

I just got OEM battery from BMW dealer today for my wife's 19" i3s, and I think mine will need new battery soon too. Therefore, I start looking for alternative b/c OEM 12v is the only thing outdated about this car. I love i3, it's a perfect car for our daily use. I read a lot about BMW i3 dead 12v, so I installed battery pigtail on both cars on the 1st day we got them. I can probably remove the pigtail if I can successfully install Ohmmu in my car.

I, too, installed a charging pigtail on the OEM battery because of how few miles we drive per month, especially during the pandemic. We didn't drive enough to keep the 12V battery's charge level high enough to avoid the "excessive discharge while parked" warning message, so I charged it with a 12V battery charger every couple of months. That's not been necessary with the Ohmmu battery because its voltage doesn't decrease much as its charge level decreases.

I was not sure about DC-DC converter charging Ohmmu battery since on the website said Absorption: 14.4 to 14.6 volts. I'm glad to hear that i3 DC-DC has no problem charging it.

The battery's BMS keeps track of its charge level by coulomb counting. Its charge level is almost always at least 99%.

The physical aspect of the battery fitment sounds difficult too, but at least I can try to modify it following your written guide.

If you need some help, send me a private message including your email address. I could send you some photos that should help with the installation.

By the way, Ohmmu G1DC22-B is a 22AH battery. Do you have to recode the car after the installation for the extra 2AH capacity over OEM?

Ohmmu explained to me that the Ah rating of a LFP battery is equivalent to about double the Ah rating of an AGM battery due to the higher output voltage and usefulness down to a lower charge level of a LFP battery. They estimated that the equivalent AGM Ah rating would be ~40 Ah.

Using BimmerCode, I set the battery type in the Body Domain Controller to "40 Ah AGM". There are only certain choices, there is no LFP battery type (only flooded-cell and AGM lead-acid), and there is no capacity choice between 20 Ah and 40 Ah. I doubt that this would make a noticeable, or maybe any, difference.

 

[neversummer]

Its sales price makes it very attractive.

I, too, installed a charging pigtail on the OEM battery because of how few miles we drive per month, especially during the pandemic. We didn't drive enough to keep the 12V battery's charge level high enough to avoid the "excessive discharge while parked" warning message, so I charged it with a 12V battery charger every couple of months. That's not been necessary with the Ohmmu battery because its voltage doesn't decrease much as its charge level decreases.

The battery's BMS keeps track of its charge level by coulomb counting. Its charge level is almost always at least 99%.

If you need some help, send me a private message including your email address. I could send you some photos that should help with the installation.

Ohmmu explained to me that the Ah rating of a LFP battery is equivalent to about double the Ah rating of an AGM battery due to the higher output voltage and usefulness down to a lower charge level of a LFP battery. They estimated that the equivalent AGM Ah rating would be ~40 Ah.

Using BimmerCode, I set the battery type in the Body Domain Controller to "40 Ah AGM". There are only certain choices, there is no LFP battery type (only flooded-cell and AGM lead-acid), and there is no capacity choice between 20 Ah and 40 Ah. I doubt that this would make a noticeable, or maybe any, difference.

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'll use bimmercode to code the same setting. 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.

Thank you again for sharing this valuable information and guidance, I'll give it a shot on the installation once arrived. I might have to pm you, so thank you in advance for your help!