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      09-04-2019, 10:29 AM   #1
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Battery Tenders / Long Term Storage

I'm planning an extended trip. I've seen here and there on the forums that if you are going to leave one of these cars for any long period of time, that it is a good idea to leave a battery tender on it to keep the battery health.

I've read that the battery in these cars are crazy expensive, and if I use the wrong charger it can destroy the battery, and they are something like $1200 to replace. I have a battery tender for my Ducati, and a Dewalt charging station that I've used on another car of mine, but I'm not sure what makes these chargers safe or not safe to use on this car.

Last edited by msdss; 09-04-2019 at 10:52 AM..
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      09-13-2019, 06:31 PM   #2
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Very good question. It must have the ability to maintain the charge, not just charge continuously. Also, must have the ability to charge AGM type batteries.

Here is a solid recommendation for a "smart" battery charger.

CTEK (56-864) MUS4.3 12 Volt Fully Automatic 8 Step Battery Charger

So, this will get you in the right direction. The cool thing with our BMW's is that you can charge from under the hood...and not the truck (where the battery actually lives)...


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      09-14-2019, 01:34 PM   #3
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+1 for the CTEK unit. I've been using it on my GT4 during the wintertime. What convinced me? Finding the Porsche's battery dead after a few weeks of sitting. Where's the battery? In the front trunk. How do you open the front trunk to access the battery to recharge it? An ELECTRIC switch next to the driver's seat. A switch that won't open the front trunk when the battery is dead. Turns out I had to connect an external power source to a special metal connector in the fuse box to be able to open the front trunk with a dead battery. Then I had to jump start the car with jumper cables, because the roadside assistance guy's battery charger didn't have the required juice to restore the Porsche battery. The official "Porsche Roadside Assistance" guy turned out to be a local third-party guy who had never dealt with this type of situation before. I googled it and we figured it out together. Nice enough guy, but he had no clue. Not very reassuring, Porsche.

So get a quality battery maintainer like the CTEK. Well worth the money!
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      09-14-2019, 01:51 PM   #4
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thanks for the replies. I'll start looking into ctek. I went and looked at the battery. it's some massive lithium ion laptop looking thing. I absolutely do not want to piss away money fixing that. much less finding myself locked out of my car because of it.
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      09-16-2019, 10:07 PM   #5
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It's not a "lithium ion laptop battery thing," it's a pretty standard (for German cars) AGM battery. There's "a thing" attached to the top that is part of the SOC (state of charge) monitoring system, and somewhere in all the mess there will be a pyrotechnic charge that fires in the event of a severe accident (this is the battery disconnect system since it isn't up under the hood like in most cars).

They are still not cheap batteries, plus if you want to not prematurely kill the replacement battery, you need to have the dealer do the swap (or someone who has access to Rheingold so they can run the "new battery who dis" procedure on the car's software). This dance is required because the car "learns" the battery's characteristics over time and adjusts charge voltage based on temperature and other factors. If you just change out a dead battery for a new one, but don't "reset" this table of learned charging factors, you end up killing the new battery much more quickly since the car ends up overvolting it (new battery doesn't need as much voltage to charge as the old one did).

The CTek chargers are solid, as are the actual "Battery Tender" brand. Just hook your tender of choice up to the posts under the hood - do NOT try to attach directly to the battery, as this would bypass any protection in the car and is the opposite of what you want to do.
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      09-25-2019, 07:28 PM   #6
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Quote:
Originally Posted by ZPrime View Post
It's not a "lithium ion laptop battery thing," it's a pretty standard (for German cars) AGM battery. There's "a thing" attached to the top that is part of the SOC (state of charge) monitoring system, and somewhere in all the mess there will be a pyrotechnic charge that fires in the event of a severe accident (this is the battery disconnect system since it isn't up under the hood like in most cars).

They are still not cheap batteries, plus if you want to not prematurely kill the replacement battery, you need to have the dealer do the swap (or someone who has access to Rheingold so they can run the "new battery who dis" procedure on the car's software). This dance is required because the car "learns" the battery's characteristics over time and adjusts charge voltage based on temperature and other factors. If you just change out a dead battery for a new one, but don't "reset" this table of learned charging factors, you end up killing the new battery much more quickly since the car ends up overvolting it (new battery doesn't need as much voltage to charge as the old one did).

The CTek chargers are solid, as are the actual "Battery Tender" brand. Just hook your tender of choice up to the posts under the hood - do NOT try to attach directly to the battery, as this would bypass any protection in the car and is the opposite of what you want to do.
Hmm. I have a bit of a dilemma. I live in a condo in downtown, and I don't have access to an electrical outlet. Considering the various battery sub-systems you've mentioned, I'm guessing I can't take the battery out and run the tender out of my condo unit (or anywhere else for that matter)?


For everyone else looking for the specific CTEK mentioned above, apparently it's been replaced by a successor, the CTEK 40-206 MXS 5.0-12 Volt Battery Charger. This is according to various reviews/answers on Amazon. I believe one of said reveiewers called CTEK to confirm, but you might want to do the same to be sure.
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      09-26-2019, 05:15 PM   #7
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I personally use a ctek multi us 7002 for my personal '17 m2 which has an AGM battery. I'm not sure if the M2C has a lithium battery, but if it does you'll need a lithium ion battery tender.
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      09-26-2019, 07:25 PM   #8
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Quote:
Originally Posted by F87source View Post
I personally use a ctek multi us 7002 for my personal '17 m2 which has an AGM battery. I'm not sure if the M2C has a lithium battery, but if it does you'll need a lithium ion battery tender.
I guess only the m3/m4 got a lithium ion? m2c is just an AGM.
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      09-26-2019, 09:02 PM   #9
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Quote:
Originally Posted by msdss View Post
I guess only the m3/m4 got a lithium ion? m2c is just an AGM.
Yeah I wasn't sure about that, the good thing is that you have a wider range of trickle chargers available and theyre cheaper.

Also Don't forget to only connect the trickle charger via the underhood jumper terminals, that way the IBS can monitor the charge and you won't risk damaging the sensor.
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      10-02-2019, 02:56 AM   #10
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Quote:
Originally Posted by gphung View Post
Hmm. I have a bit of a dilemma. I live in a condo in downtown, and I don't have access to an electrical outlet. Considering the various battery sub-systems you've mentioned, I'm guessing I can't take the battery out and run the tender out of my condo unit (or anywhere else for that matter)?
You could take the battery out and put it on a tender outside of the car, but that will then piss off all of the systems in the car since they lose power. They should mostly (if not fully?) figure that out when you hook it back up to the car though.

The concern about attaching the tender directly to the battery is only a concern if the battery is still in the car. You don't want to do that because it can damage the car's charge monitoring stuff (in theory, although I don't know if anyone's actually done that).
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      10-02-2019, 08:45 AM   #11
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Quote:
Originally Posted by ZPrime View Post
You could take the battery out and put it on a tender outside of the car, but that will then piss off all of the systems in the car since they lose power. They should mostly (if not fully?) figure that out when you hook it back up to the car though.

The concern about attaching the tender directly to the battery is only a concern if the battery is still in the car. You don't want to do that because it can damage the car's charge monitoring stuff (in theory, although I don't know if anyone's actually done that).
Edit- I didn't read the previous post correctly.

Correct, but you don't necessarily need to remove it, of you do make sure you're using a battery tender that can monitor voltage vs. a standard battery charger. This approach is not ideal as it'll charge the battery more than the IBS would.


Correct, damage only occurs if you attach a charger directly the the battery itself if it's in the car. This is because it bypasses the IBS and can over charge the battery. Also if you're not using a voltage stable battery tender the pulses in the current delivery can damage the IBS itself.
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      08-14-2021, 01:58 AM   #12
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Quote:
Originally Posted by F87source View Post
Edit- I didn't read the previous post correctly.

Correct, but you don't necessarily need to remove it, of you do make sure you're using a battery tender that can monitor voltage vs. a standard battery charger. This approach is not ideal as it'll charge the battery more than the IBS would.


Correct, damage only occurs if you attach a charger directly the the battery itself if it's in the car. This is because it bypasses the IBS and can over charge the battery. Also if you're not using a voltage stable battery tender the pulses in the current delivery can damage the IBS itself.
So I dumbassed this and charged on the battery directly. I am trying to find out if I damaged the battery or IBS. Any idea on how to check?
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      08-14-2021, 02:08 AM   #13
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Quote:
Originally Posted by Megator View Post
So I dumbassed this and charged on the battery directly. I am trying to find out if I damaged the battery or IBS. Any idea on how to check?
Yeah this is pretty common, and when I was new to this platform I did it on my m235i as well. Since it was with my CTEK mus 7002 it was fine as it was microprocessor controlled and monitors voltage, and comes with a low ripple rating to prevent electronic damage. Zero issues with the battery as it was never over charged (had the car for a couple of years and zero problems with that battery even in the winter), and IBS had zero issues as diagnosed below.


1) This is the most important one, but what charger did you use? If you used a low ripple charger that is microprocessor controlled to not over charge then the chance of damage to the IBS is literally almost zero. If you used a really crappy charger the chances of damage are higher, and if you jump started the car you have an extremely high chance of frying the IBS. If your charging and jump started had a surge or alot of sparking then there is a huge chance your IBS is dead.


In most cases the battery will be absolutely fine, unless your charger doesn't stop charging and just keeps force feeding the battery.


2) To check if everything is ok here is what you should do:

a) For the IBS check ISTA, if ISTA doesn't show any codes and can stilll report a battery voltage that matches what your multi meter reads (while the car is in accessory mode) you should be fine. There are also ISTA diagnostic procedures to check if the IBS is ok as well, and you can run that.

But if no errors are reported the IBS is fine. Also check it to see if there is any physical damage.


b) For the battery check it with a multi meter is the voltage within normal range? If yes you are ok. Then check the physical shape of the battery - is it warped or swollen, are the terminals damaged? if not you should be fine. The battery should be the toughest part of the system and if it didn't blow up, catch on fire, or warp/bulge, and or melt from over charging and surging you are fine.
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      08-14-2021, 03:16 AM   #14
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Quote:
Originally Posted by F87source View Post
Yeah this is pretty common, and when I was new to this platform I did it on my m235i as well. Since it was with my CTEK mus 7002 it was fine as it was microprocessor controlled and monitors voltage, and comes with a low ripple rating to prevent electronic damage. Zero issues with the battery as it was never over charged (had the car for a couple of years and zero problems with that battery even in the winter), and IBS had zero issues as diagnosed below.


1) This is the most important one, but what charger did you use? If you used a low ripple charger that is microprocessor controlled to not over charge then the chance of damage to the IBS is literally almost zero. If you used a really crappy charger the chances of damage are higher, and if you jump started the car you have an extremely high chance of frying the IBS. If your charging and jump started had a surge or alot of sparking then there is a huge chance your IBS is dead.


In most cases the battery will be absolutely fine, unless your charger doesn't stop charging and just keeps force feeding the battery.


2) To check if everything is ok here is what you should do:

a) For the IBS check ISTA, if ISTA doesn't show any codes and can stilll report a battery voltage that matches what your multi meter reads (while the car is in accessory mode) you should be fine. There are also ISTA diagnostic procedures to check if the IBS is ok as well, and you can run that.

But if no errors are reported the IBS is fine. Also check it to see if there is any physical damage.


b) For the battery check it with a multi meter is the voltage within normal range? If yes you are ok. Then check the physical shape of the battery - is it warped or swollen, are the terminals damaged? if not you should be fine. The battery should be the toughest part of the system and if it didn't blow up, catch on fire, or warp/bulge, and or melt from over charging and surging you are fine.


1) I didn't jump the car luckily. I used a CTEK on it and a dumb rando charger the shop that bench unlocked my car had (a whole 'nother issue...). The dumb charger would have been on there a couple min max. The car started after that and seemed to drive OK with no errors on the dash etc.

2) Ill see if I can get ISTA on it today. Everything looks ok at the battery / IBS side but the sticker on the battery does look a little bubbly... The battery was on a CTEK charger all night and read 12.22V this morning and was at stage 6 (float) of the charging cycle.
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      08-14-2021, 03:24 AM   #15
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Quote:
Originally Posted by Megator View Post
1) I didn't jump the car luckily. I used a CTEK on it and a dumb rando charger the shop that bench unlocked my car had (a whole 'nother issue...). The dumb charger would have been on there a couple min max. The car started after that and seemed to drive OK with no errors on the dash etc.

2) Ill see if I can get ISTA on it today. Everything looks ok at the battery / IBS side but the sticker on the battery does look a little bubbly... The battery was on a CTEK charger all night and read 12.22V this morning and was at stage 6 (float) of the charging cycle.
Yeah definitely get ista on it, the errors could be hidden codes where the car still can charge the battery but doesn't know extractly the state of the battery but it's not enough of an issue to cause a full check engine light.


What ctek mode did you use? Make sure it's for agm.


The bubbly sticker could be the sticker peeling off due to moisture. If the battery isn't too obviously swollen it should be fine.
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      11-11-2021, 11:46 PM   #16
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Battery tender for the winter

My 2020 M2 is tucked comfortably away for the winter with a ctek 5.0 AGM battery tender connected to posts under the hood. Can I safely leave that attatched all winter, or until the next opportunity for M2 fun comes along?
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      11-12-2021, 12:08 AM   #17
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Quote:
Originally Posted by Tachycardia View Post
My 2020 M2 is tucked comfortably away for the winter with a ctek 5.0 AGM battery tender connected to posts under the hood. Can I safely leave that attatched all winter, or until the next opportunity for M2 fun comes along?
Yes, as long as you have the tender in the correct settings for your battery and have not left it in supply mode.
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      11-12-2021, 12:36 AM   #18
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Thanks

Thanks for reply. I have it set for AGM, but will double check it in AM.
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      11-12-2021, 12:39 AM   #19
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Thanks for reply. I have it set for AGM, but will double check it in AM.
No problem. I would also suggest getting a surge protector just incase.
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      11-12-2021, 12:42 AM   #20
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Thanks. I was thinking of the same thing. You a night owl or out west where it is not that late?
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      11-12-2021, 12:52 AM   #21
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Quote:
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Thanks. I was thinking of the same thing. You a night owl or out west where it is not that late?
Both lol! I stay up super late (usually till 3 or 4 am) doing work or just chilling.
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      11-13-2021, 01:45 AM   #22
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ctek 5.0

Looked at this when I got home this morning. I do not see an indication for "supply" mode. the options are motorcycle, car, AGM, and recondition. Mine is on car and AGM. I suspect recondition is "supply" mode. Busier tonight since it is Friday (party) night and the roads are wet.
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