12 volt battery depleted

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stohje

New member
Joined
Jul 22, 2020
Messages
4
So I'm an idiot. I used our 2015 i3 REX with 14k miles to power an air compressor to blow up some pool floats over the weekend. I did not start the car completely, I left it in accessory mode (or whatever). I noticed the "Excessive Battery Discharging While Parked" error close to the end of using the compressor so I did start the car all the way. I then locked the car and went about my business. Monday morning on the way to work I noticed the auto open lock didn't work when I grabbed the handle, the unlock button on the key worked fine. I of course then got the same error when starting the car. I googled the issue and couldn't find much about recharging the battery, lots about replacing it. Oh and I HAD NO IDEA the i3 had a 12volt battery!!! Seems odd to me hat an electric car would need one. I did find a BMW service bulletin that appeared to say the fast charger would recharge the 12volt. So I've been plugging the car in every night when I get home (use about 12-15 miles electric range daily) and am still getting the error. No issues yet with starting or driving the car but I'm concerned about long term problems.

Questions:
Does the 12v battery need replacement? Or Will it eventually recharge?
Is there a way to tell if the 12v is being charged by the main battery (which i understand is the process)?
Is there a way to see the charge level of the 12v?
I used Bimmercode to enable the full gas tank and a few minor tweaks (decrease lock beep volume etc.) a few months ago, so not sure if that's a problem?

Any advice would be much appreciated!
 
Yes, when the car is 'active' the DC/DC converter charges the 12v battery from the HV battery pack. When the battery gets to the point that it won't hold that charge, with a low voltage you get the warning. You may have triggered the warning with the battery low because you depleted the charge filling the pool toys. The DC/DC converter will charge it back up. Is the car still giving you the warning? If the warning repeats, it means the battery will no longer hold a full charge because it is is failing due to age, and needs to be replaced. Average life of the i3 12v battery is around four to five years. Only way to see the charge and health of the battery is with a battery tester. This is the one I use: https://www.amazon.com/gp/product/B07ZT49LX7/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
 
stohje said:
Does the 12v battery need replacement? Or Will it eventually recharge?
I'm pretty certain that the DC-DC converter should have turned on to recharge your 12 V battery. This occurs on our 2014 BEV when the 12 V system is on even when the car is off. I suspect that your 12 V battery is failing and needs replacing. A replacement can be purchased from an East Penn Manufacturing retailer for considerably less than the typical BMW dealer cost. Installing it is pretty easy as well. BMW dealers charge several hundred dollars to replace the 12 V battery.

stohje said:
Is there a way to tell if the 12v is being charged by the main battery (which i understand is the process)?
Not without measuring the 12 V system voltage which would be ~14.3 V when the 12 V battery is being charged. I have an inexpensive 12 V voltmeter plugged into the auxiliary power port below the center of the dashboard for this purpose.

stohje said:
Is there a way to see the charge level of the 12v?
Unfortunately not. The DC-DC converter in our i3 is very aggressive charging the 12 V battery so that even with a voltmeter, it's very difficult to measure the resting voltage of the 12 V battery.
 
Thank you both so much for the quick responses!
You pretty much confirmed my suspicion the battery needs replacement, darn! I've been plugging it in nightly and the auto unlock works in the morning but not when I leave work so that seems pretty definitive also. (my '05 M3 did some truly bizarre things that didn't seem obvious that its battery was almost done).

I was watching videos on youtube that show how to replace, didn't look too hard. I've never replaced a battery myself, so wondering if it's easy to do without getting shocked (assuming I don't get super clumsy and grab both poles at the same time). The fiddly drain pipe bit looks like a pain though.

Thanks again!
 
stohje said:
I've never replaced a battery myself, so wondering if it's easy to do without getting shocked (assuming I don't get super clumsy and grab both poles at the same time). The fiddly drain pipe bit looks like a pain though.
12 volts is insufficient to push electrical current through one's body, so you could grab both terminals with no risk of electrocution. Also, there is no high-voltage risk, either.

Although doing so is apparently unnecessary, I will disconnect the high-voltage disconnect before I replace the original 12 V battery in our 2014 BEV (I have a replacement waiting on a shelf). I'll be following these instructions.
 
The link to the instruction is OK but the actual instructions are not very good. The writers of this document did a lousy job. Not very concise, clear or easy to follow or maybe its me....
 
Timjohn said:
The link to the instruction is OK but the actual instructions are not very good. The writers of this document did a lousy job. Not very concise, clear or easy to follow or maybe its me....
The NewTIS site might be identical or very similar to BMW's TIS site and is the only source of BMW repair information that I've found. I think these are typical of hyperlinked instructions. The same steps occur in multiple tasks, so rather than repeating these same steps in each task, hyperlinks refer to the steps. I've gotten accustomed to this style and am happy to have it since workshops manuals on CD's, DVD's, or paper are not available for the i3.
 
You can check in your area for an East Penn Manufacturing distribution warehouse - they are the OEM supplier (Transportation Division) of the BMW i3 AUX 18L battery. They will sell over-the-counter. https://www.eastpennmanufacturing.com/contact/where-to-buy/

Remy sells the East Penn brand i3 battery on line under their Remy name as well - though their online price seems to have jumped from around $120 to $220 recently.

You might even check with local BMW dealers. Some owners have reported actually getting both reasonable battery price and replacement price quotes.
 
I replaced mine proactively a couple of months ago, it's not that hard to do. Some people have had issues after replacing it like the car throwing error codes and it seems this is because if you don't charge the battery before replacing, if it's discharged when you install it, it could be a problem. The work around is to fully charge it before replacing it. Here is a good YT video on how it's done.

https://www.youtube.com/watch?v=Ee36vWXMHBg
 
Thanks for all the great info!
I couldn't find a local retailer for the OEM battery so ordered it from REMY. Should be here on Thursday. I absolutely LOATHE my local BMW dealer. Gotten much worse in the time since we leased the i3. They treat you like a loser if you try to haggle at all (and we've bought 3 cars there). Tried to get me for ~$1,000 in "safety inspections" etc. at lease end when we purchased car. BMW corporate sent me a notice that the residual on the lease would be reduced by ~$10k. So I used that as a test for the dealership. They were going to charge full residual until I showed them the letter from corporate. The finance person then did the "let me talk to my manager" thing and came back 15 minutes later with the great news that they would honor that price. Then talked about the safety inspections etc costs. We just use the car for in town commuting and only had ~12k on the odo at the time and had been serviced recently. So I kept the dealer on the hook (texting back and forth a bit) for a couple days then texted them we were going with corporate. Zero communication after that, no "okay thanks for your business", "let us know how we can help in the future" etc. Crap customer service. <END RANT>
Has anyone found non-dealer mechanic/service options for the i3 in their area? We have several BMW/European specialist mechanics locally but none do i3. Guessing local shops don't want to invest time/money in equipment and training for a fairly low volume vehicle...

Thanks again, I'll let you know how the battery install goes.
 
Has anyone found non-dealer mechanic/service options for the i3 in their area? We have several BMW/European specialist mechanics locally

I found a good well reviewed independent BMW service garage near me, run by two former dealer/factory BMW mechanics (they only service BMWs). They are not i3 trained, but more than willing to do the normal oil/brake fluid/brake pads, etc. service - at rates lower than the BMW dealership. I think if something goes wrong with the i3 specific 'bits'' it might be dealer-only, though.
 
THere are various scan tools that can read the BMW specific error/status codes, so, with some knowledge, you do not need to be a BMW dealer's shop to at least be able to get an idea what may need fixing. Things like brakes are pretty straight forward as are the suspension bits. If you have the REx, an oil change isn't rocket science, nor is the muffler. There are some strange bits in the fuel system, and they may not be competent to deal with charging or battery issues, but that's not a given, either. Consider, though, that in a dealership, they may only have had a few of their techs trained on the i3, so as a system, not every tech can deal with them. When it might come to body work, especially when it might involve the CFRP chassis, probably best to not deal with other than the factory trained people (and I'm not sure they can get all of the frame parts, either).
 
Thanks for the reply Mark. I was surprised the top independent BMW mechanic in the area wouldn't do the simple things you mentioned. Too bad since the rex seems to need an oil change every week or so! :D Haven't checked with all locals so I'll keep trying.

Battery update:
Ran many errands today and got the battery warning once early on but didn't get it again. So weird. Maybe it was slowly recharging throughout the week. If it stays good, at least I'll have a spare when this one does finally quit completely.
 
Too bad since the rex seems to need an oil change every week or so! :D

Once a year doesn't' seem too bad to me. My previous ICE vehicle needed one about every four to six months. :cry:
 
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accessory battery long term storage
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r/BMWi3
•Posted byu/pleung6
6 hours ago
accessory battery long term storage
I want to share my experience with my 2017 bmw i3 with regards to long term storage.
Here are the facts:
Car unplugged in garage. March 20 123 mile capacity, April 20. 118 mile capacity, June 19 115 mile capacity (91%), Sept 20 105 mile ,
capacity, These measurements were taken by my friend who checked on the car. The car started no problem on Sept 20 ( 6 full months left unplugged) . He took it for a 35 mile drive ( theoretically to charge the accessory battery) and returned to the garage unplugged and store further reading 85 mile capacity (62%).
Before I left, I spoke with BMW service/mechanic in Scottsdale (Penske BMW) who said that the accessory battery will trickle charge by itself from the high voltage battery. Also, the manuals recommendation to leave it plugged in for long term storage is only because leaving it 100 percent charged is the lesser evil than unplugged and risking discharge to 0. Both are actually undesirable for lithium battery permanent capacity loss . The best discharge rate is between 75 % down to 60% for the battery and I was able to achieve this because I had a friend checking on the car to ensure it will not go below 60 (otherwise he would plug it in for me which did not happen).
There was no need to remove the accessory battery and trickle charge it (difficult to do for the average person).
I really however would like a high level BMW engineer to confirm thru this thread that indeed the accessory battery is trickle charged from the high voltage battery when placed just in storage unplugged. Because other than verbal from the mechanic, I cannot for the life of me find anywheres on the internet or in any other forum this statement. This has led to much advice regarding diving into the front of the car and risking high voltage shock and removing the accessory battery to attach a trickle charge to it. So please if anyone who has formal training in the design of this car's electronics, please confirm this mechanic's statement that the accessory battery is indeed trickle charged by the high voltage battery when left unplugged.
P.
 
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