12 V battery replacement suggestions needed

[alohart]

The original 12 V battery in our 1 August 2014 i3 BEV shows no signs of failing. However, many owners of i3's of similar age or even newer are reporting failed 12 V batteries that have left some stranded which I want to avoid. My only local source of a replacement 12 V battery that I could pick up immediately is my BMW dealer whose price for this battery is quite high.

Therefore, I sent a message from East Penn Manufacturing's Website asking how I could order an AUX18L battery after several attempts to contact East Penn's local distributor failed. As a result, a local East Penn battery retailer contacted me. I placed an order for an AUX18L battery for ~$60 less than the BMW dealer's price. I just picked it up.

I now have several options:

1. I could replace the original battery immediately, and

a. I could return it to the retailer to receive a refund of my $20 core charge, or

b. I could keep it as an emergency replacement battery for when my new battery fails.

2. I could continue using my original battery until it fails.

If I choose 1, I would be protected from failure during the entire 12-month warranty. However, this isn't particularly important to me because I can't recall ever having a battery replaced under warranty. With no temperatures extremes here, a 12 V battery has a pretty easy life.

If I choose 1a, I would hate to discard an apparently healthy battery prematurely. However, this would be the easiest choice and would make my wallet $20 fatter if I return my old battery within 6 days.

If I choose 1b., I would need to charge my old battery probably annually to keep it healthy, but there's no guarantee that it wouldn't fail while being stored. However, this would theoretically give me time to order a replacement which took ~3 weeks to arrive here in the middle of the Pacific Ocean.

If I choose 2, I would not concerned about my new battery weakening in storage because an AGM battery has a very long shelf life and very low self-discharge rate. I would charge it annually to prevent it from self-discharging too much. However, when my new battery fails, I would not have an emergency battery to install.

I kind of like having an emergency battery available since it takes several weeks to order a replacement unless I would be willing to pay the BMW tax on a new battery purchased from my dealer (they currently keep several in stock).

What would you do?

 

[Srivenkat]

Aloha Art,

As you note as well, AGM batteries have a long life. My 2007 Camry Hybrid is still on its 2006 installed battery. My 2010 Prius was still on its original when it recently got totalled as well.

Does the 12V have the same easy life as in the Prius in which it simply connects the HV battery to the car apart from running miscellaneous ancillaries? If so, unless you inadvertently deep-discharged your 12V by leaving cabin lights on and such, I think the 12V could last a decade+.

I would be worried like you if the i3 can't be "jumpstarted" if the 12V happens to ever die on the road (usually there are warning signs in typical use, of the 12V failing). If it can't be jumpstarted, using something like the below, then I would probably change it once a decade as preemptive maintenance.
And I would really be worried if even the local dealer didn't stock the battery, albeit at a higher price than online.

https://www.amazon.com/jfegwo-Portable-Battery-Starter-Compressor/dp/B074FS69F9/ref=sr_1_3?crid=HVDSRDFCU7AK&keywords=liion+jump+start&qid=1556926493&s=gateway&sprefix=LiIon+jump%2Caps%2C149&sr=8-3

 

[vreihen]

Do any of the chain auto parts stores offer free load testing of batteries out there in paradise? Assuming that their tester doesn't laugh at the small battery capacity and gives a numeric output (and not just a pass/fail light), you can have them pull a load test on both factory and replacement AUX18L so you can judge the relative conditions of both and decide which one to put back in.....

 

[jadnashuanh]

I think you'd need some specialized equipment to test the 12vdc battery in the i3. There are no big loads like a starter, and testing the charging circuit isn't like testing a typical alternator on an ICE or hybrid. You might end up having to remove it, and that labor probably isn't something they'd want to do for free. I could be totally wrong on this, doesn't hurt to ask, but considering they could do some damage...I'd be a bit leery.

The BMW computers can probably tell when that battery is getting weak. That routine is (I think) available to other computer testers for after market, but aren't especially cheap.

 

[i3daytonoh]

My 2013 dated battery still works like new. If I did not know the prior history of my car, I would consider replacing it to prevent an unexpected failure. If it was my decision, I would probably keep using the original battery and place the new battery on a low power battery maintainer for future use. Keep us updated on your decision.

 

[vreihen]

Another thought that I just had. If you don't already have an AGM-type battery maintainer/charger, I suspect that buying one to maintain the old battery as a spare will exceed the $60 BMW tax for the privilege of buying a new battery from them in an emergency.

FWIW, I am [DMV willing!] picking up a new-to-me i3 today, and the first thing that I'm going to do as soon as it's sitting in the driveway is order an AUX14L to replace the BMW one. The 12V battery seems to be the Achille's heel of the BEV model from what I've read so far.....

 

[Srivenkat]

In the beginning of my 2010 Prius ownership, I became obsessed with the health of the 12V, so I got the below (compatible with AGM batteries) and would routinely put the 12V (both on the Prius and my Hybrid Camry) on it just as a preventative measure, since our trips are short (<5miles). After a couple of times doing it, the interest faded and I neglected doing it but the batteries have held up fine.

https://www.amazon.com/CTEK-56-864-Automatic-Battery-Charger/dp/B006G14FK8

To me, an old battery, hopefully only insignificantly degraded, is a tried and tested one and is preferable to a new one. So, I would carry the new one in the frunk, just in case you are stranded somewhere.

 

[RonRPH]

I have ordered the 12volt replacement battery since a lot ( my impression) seem to fail around the four year mark. Ordered a battery tender at the same time and have it hooked up to that. And now I've gotten maybe a bit lazy. I see no signs of the current one failing and have decided just to wait. I'll replace it if/when I see signs of failure. I intend to hook the new one up with a battery monitor- maybe I can tell when it is starting to fail. I really believe that one of the failures of these cars is not having some sort of emergency power port that you could hook a jumper box to in the event the 12 volt fails.

 

[Srivenkat]

I suspect most of the 12V battery failures on the i3 are a result of the battery being allowed to go dead once or twice (which could easily happen on a dealer lot) which severely impacts the life of the battery.

A couple of options if one would like to wait for the actual degradation of the battery before replacing for environmental reasons and such:

1. install a low-voltage autodisconnect switch which I tried on my Prius and documented here:

https://priuschat.com/threads/12v-battery-low-voltage-auto-disconnect.132609/

This is assuming the frunk opens when the 12V is not connected, so one could reach the switch and reset it. It might also be possibe to improvise the installation such that the switch is in the frunk. Is there a manual frunk release? As you can tell I am still looking for a deal on the i3.

2. Carry a replacement 12V in the frunk that could be connected to the installed 12V when it's dead. Since the 12V is not easily reachable, perhaps a combination of the cables on the below page can help bring a connection point into the frunk to which the replacement 12V can momentarily be connected?

https://smartercharger.com/collections/accessories

For example, I would imagine the below can be connected in series:

https://smartercharger.com/collections/accessories/products/ctek-comfort-connect-m8-1
https://smartercharger.com/collections/accessories/products/ctek-comfort-connect-cig-socket

then connected with another third party cable such as the below that connects the replacement 12V into the cig socket?

https://www.amazon.com/SPARKING-Cigarette-Terminal-Assembly-Extension/dp/B0771KNFBF/ref=sr_1_15_sspa?keywords=cigarette+adapter+to+cigarette+adapter&qid=1556985275&s=automotive&sr=1-15-spons&psc=1

 

[Anonymous]

I really believe that one of the failures of these cars is not having some sort of emergency power port that you could hook a jumper box to in the event the 12 volt fails.

If the 12 volt battery hasn't totally failed to where it won't pass a charge across the plates or accept a charge, if you plug the car in to charge, this will also charge the 12 volt battery. People with a 'dead' car due to the 12 volt battery end-of-life, have been able to plug the car in overnight, and have enough of a charge in the 12 volt to start the car and drive to the dealership next day.

 

[vreihen]

Is there a manual frunk release? As you can tell I am still looking for a deal on the i3.

With a disclaimer that I'm one step further than you in the purchase process (made a killer deal and have one of the key fobs but not the car or plates yet thanks to DMV closing early), there is an official BMW North America video on YouTube showing a hidden frunk release cable loop tucked in behind a snap-out trim cover right under the frunk/trunk opener buttons. Don't know if it is there in the production cars though, or if it is possible to open the doors with a dead battery to get to that emergency release cable.....

https://www.youtube.com/watch?v=012oYotZA2g

 

[alohart]

Does the 12V have the same easy life as in the Prius in which it simply connects the HV battery to the car apart from running miscellaneous ancillaries? If so, unless you inadvertently deep-discharged your 12V by leaving cabin lights on and such, I think the 12V could last a decade+.

I owned a 2000 Honda Insight hybrid for 15 years. Its small 12 V battery performed similar functions to what you describe for a Prius or for our i3. However, in Honda's attempt to maximize efficiency, the DC-DC converter didn't charge the 12 V battery until its voltage dropped significantly or until the 12 V current exceeded a certain level (e.g., with the headlights on). The result was that the average charge level of the 12 V battery was low enough to shorten its life even when I replaced the original flooded-cell battery with a series of AGM batteries. So how the charging system functions affects the life expectancy of the 12 V battery.

For over 2 years, I have had a 12 V voltmeter plugged into the auxiliary power port below the climate control system controls. I have been surprised by how low the 12 V voltage drops when the high-voltage system is booting before the DC-DC converter begins charging the 12 V battery (I have confirmed the voltmeter voltage by comparing the voltage at the battery's terminals). It's difficult to measure the resting voltage because opening a door, the hood, etc., fires up the high-voltage system. However, the DC-DC converter seems to remain on while driving and is on while actively charging the Li-ion battery pack, so the 12 V battery's average charge level should be pretty high unless an i3 isn't driven frequently. However, because the 12 V system voltage usually drops below 12.0 V when the high-voltage system is booting before the DC-DC converter turns on, the 12 V battery must be delivering considerable current while the high-voltage system is booting. Maybe this shortens its life over time.

I would be worried like you if the i3 can't be "jumpstarted" if the 12V happens to ever die on the road (usually there are warning signs in typical use, of the 12V failing).

Traditional jump-starting risks damaging the DC-DC converter and maybe other high-voltage system electronics. However, it's easy to disconnect the high-voltage system. The 12 V battery could then be charged without worrying about damaging something. However, with the high-voltage system disconnected, an i3 cannot enter drive readiness state, so this wouldn't be a "jump-start".

If it can't be jumpstarted, using something like the below, then I would probably change it once a decade as preemptive maintenance.

It's too early to know, but I would be surprised if any i3 12 V batteries last 10 years. I suspect many have been allowed to discharge to the point of damage while parked on a dealer's lot even though dealers are supposed to maintain these batteries. The 12 V vampire loads like the burglar alarm, the keyless entry system, the entertainment system clock, etc., can discharge the 12 V battery low enough in 6 weeks or so that entering drive readiness state is not possible before charging the 12 V battery.

 

[alohart]

Do any of the chain auto parts stores offer free load testing of batteries out there in paradise?

Might be worth checking although the chain would almost certainly not have a replacement battery to sell me, so I don't know whether they would spend the time on a free load test. Supposedly, BMW's diagnostic software is able to determine the health of an i3's 12 V battery. The original battery in our i3 tested "normal" during our most recent scheduled maintenance visits in November, 2018.

To safely perform a load test, the high-voltage system would need to be disconnected (quick and easy). BMW recommends using the 12 V terminals under the cargo area floor cover, probably because the 12 V battery terminals aren't very accessible.

 

[alohart]

If it was my decision, I would probably keep using the original battery and place the new battery on a low power battery maintainer for future use.

Due to an AGM battery's very low self-discharge rate, it isn't necessary to keep an AGM battery on a battery maintainer during storage. I would probably charge it annually.

Keep us updated on your decision.

Will do.

In ~3 weeks, I will be storing our i3 for ~3.5 months. As I have done in the past, I will disconnect the 12 V battery's negative cable to prevent it from discharging, and then fully charge it. I wanted to have a new 12 V battery available when we return in case the original battery dies during storage which seems unlikely.

I'm leaning toward running the original 12 V battery until it either dies or a warning about a weak 12 V battery is displayed. If it dies while we are away from home, I'll order a ride-sharing car to take me home to pick up my new battery and the tools necessary to replace the battery. Living on an island, I can never be far from home.

 

[alohart]

If you don't already have an AGM-type battery maintainer/charger, I suspect that buying one to maintain the old battery as a spare will exceed the $60 BMW tax for the privilege of buying a new battery from them in an emergency.

Correct! However, I already own a nice Swedish CTEK US 0.8 12 V battery charger suitable for charging a 12 V 20 Ah AGM battery, so I have what I need.

FWIW, I am [DMV willing!] picking up a new-to-me i3 today, and the first thing that I'm going to do as soon as it's sitting in the driveway is order an AUX14L to replace the BMW one. The 12V battery seems to be the Achille's heel of the BEV model from what I've read so far.....

Make sure to specify an "AUX18L". Deka also makes an AUX14 which would not be the correct battery.

I wouldn't describe the i3's 12 V battery as its Achille's heel (both BEV and REx models react to a weak 12 V battery in the same way). Unlike with an ICE vehicle, there is no slow starter motor to provide a warning of a weak 12 V battery, so a weak 12 V battery could go unnoticed.

i3 owners need to be aware of what to do when the 12 V battery is too weak to allow an i3 to enter drive readiness state. As described in the Owner's Manual, plugging in an EVSE would also charge the 12 V battery when charging is active (i.e., the Li-ion battery pack isn't full). That could be sufficient to allow an i3 to drive to a dealer for a 12 V battery replacement unless one plans to DIY. If charging with an EVSE is insufficient or not possible, charging the 12 V battery with a battery charger would be the next step. However, jump-starting isn't recommended because high-voltage electronics could be damaged.

 

[alohart]

I have ordered the 12volt replacement battery since a lot ( my impression) seem to fail around the four year mark. Ordered a battery tender at the same time and have it hooked up to that.

No need to attach a battery tender to an AGM battery due to its very low self-discharge rate and thus long shelf life. The AUX18L battery I just bought had been sitting on a shelf somewhere since it was manufactured in June, 2018, and was still at ~70% charge level. I have charged it to full and won't do so again for another year.

I intend to hook the new one up with a battery monitor- maybe I can tell when it is starting to fail.

About 2 years ago, I installed a 12 V voltmeter in the auxiliary power port below the climate control system controls. Because the DC-DC converter turns on so often to charge the 12 V battery, it's quite difficult to measure the resting voltage of the 12 V battery. The only way I was able to do this was to run the long leads of a voltmeter up through the underside of the car to the 12 V terminals below the cargo area floor cover so that I did not have to open a door, the frunk, or the hatch, all of which would have turned on the DC-DC converter, to measure the voltage. After several hours of not touching the car, I was able to measure the resting voltage.

I really believe that one of the failures of these cars is not having some sort of emergency power port that you could hook a jumper box to in the event the 12 volt fails.

Jumping an i3 risks damaging the DC-DC converter or some other high-voltage electronics, so it's not recommended. After disconnecting the high-voltage system (quick and easy), charging the 12 V battery is safe to do, but an i3 won't enter drive readiness state with the high-voltage system disconnected, so this isn't a jump-start.

 

[alohart]

A couple of options if one would like to wait for the actual degradation of the battery before replacing for environmental reasons and such:

1. install a low-voltage autodisconnect switch which I tried on my Prius and documented here:

https://priuschat.com/threads/12v-battery-low-voltage-auto-disconnect.132609/

This is assuming the frunk opens when the 12V is not connected, so one could reach the switch and reset it. It might also be possibe to improvise the installation such that the switch is in the frunk. Is there a manual frunk release? As you can tell I am still looking for a deal on the i3.

There is a manual frunk release. However, if it's like other i3 manual release cables, it's fragile plastic intended for emergency use only.

Also, the high-voltage disconnect should probably be opened before disconnecting the 12 V battery, so using an autodisconnect switch might not work well. The BMW Technical Information System suggests that an i3 software update in 2014 might have removed this requirement, but I wouldn't risk it.

2. Carry a replacement 12V in the frunk that could be connected to the installed 12V when it's dead. Since the 12V is not easily reachable, perhaps a combination of the cables on the below page can help bring a connection point into the frunk to which the replacement 12V can momentarily be connected?

I would not want to carry an extra 18 lb. in the frunk at all times even if it were suitably constrained. I don't think that the threat of a dead 12 V battery is serious enough to justify carrying the extra weight and having live cables lying around. However, some i3 owners might be more worried than I am because I can never be far from home living on an island.

 

[Srivenkat]

It's difficult to measure the resting voltage because opening a door, the hood, etc., fires up the high-voltage system.

Does this mean the HV (high-voltage) battery is connected (and disconnected after a while) everytime the door/hood is opened? I thought this would happen only when the i3 is "start"ed with the foot on the brake pedal.

I would be worried like you if the i3 can't be "jumpstarted" if the 12V happens to ever die on the road (usually there are warning signs in typical use, of the 12V failing).

Traditional jump-starting risks damaging the DC-DC converter and maybe other high-voltage system electronics. However, it's easy to disconnect the high-voltage system. The 12 V battery could then be charged without worrying about damaging something. However, with the high-voltage system disconnected, an i3 cannot enter drive readiness state, so this wouldn't be a "jump-start".

How about carrying the replacement 12V in the car and then connecting it to the 12V terminals either up front or under the cargo cover? This shouldn't entail any risk of damage right?

Also, I am curious to hear your thoughts on using a low-voltage autodisconnect switch to warn of a severely degraded battery that should be replaced soon.

 

[jadnashuanh]

FWIW, the car disconnects the 12vdc sockets from the battery after awhile.

All of the control electronics in the car are controlled by the 12vdc circuit. If that were disconnected, nothing else would work in the car. There is a secondary circuit in the charging circuit that will try to regenerate the 12vdc battery so it can then power the computers normally. That only works if it is connected to an EVSE.

 

[RonRPH]

Hi Art.
No need to attach a battery tender to an AGM battery due to its very low self-discharge rate and thus long shelf life. The AUX18L battery I just bought had been sitting on a shelf somewhere since it was manufactured in June, 2018, and was still at ~70% charge level. I have charged it to full and won't do so again for another year.
- from BatteryStuff.com on AGM batteries. DO: Keep the battery as fully charged, as often as possible. I don't have it on a battery charger or trickler - it's a tender- it will only charge the battery as needed.

About 2 years ago, I installed a 12 V voltmeter in the auxiliary power port below the climate control system controls. Because the DC-DC converter turns on so often to charge the 12 V battery, it's quite difficult to measure the resting voltage of the 12 V battery. The only way I was able to do this was to run the long leads of a voltmeter up through the underside of the car to the 12 V terminals below the cargo area floor cover so that I did not have to open a door, the frunk, or the hatch, all of which would have turned on the DC-DC converter, to measure the voltage. After several hours of not touching the car, I was able to measure the resting voltage.
- I tried this also. And just gave up after awhile. I'm hoping to get better results from a bluetooth one connected right on to the battery (I'll install it with new battery if I can)

Jumping an i3 risks damaging the DC-DC converter or some other high-voltage electronics, so it's not recommended. After disconnecting the high-voltage system (quick and easy), charging the 12 V battery is safe to do, but an i3 won't enter drive readiness state with the high-voltage system disconnected, so this isn't a jump-start.
- I understand this and would never try to jump the car. But could not this be a designed in feature? I thought ( and I could be wrong) I had read once where somebody hooked one up somewhere in the rear compartment.