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Discussion Starter · #1 ·
Hi -
I have a 2015 Fortwo ED and recently my car started dying if it wasn't driven every day. I took it in for its yearly check-in and the dealer confirmed I needed a new 12v, but that nothing else was wrong. I replaced the 12v battery but I am still having the same issue!

Has anyone else experienced this issue?

Thank you!
 

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MY08 cabrio MY09 Brabus MY21 Bolt
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I replaced the 12v battery but I am still having the same issue!
Welcome to SCoA!

What group number is your NEWLY purchased 12V?

Did the parts house confirm the new battery’s voltage as something in excess of 12.6V?

It is not uncommon for a “fresh” battery to have a dead cell or not be fully charged.

Caution, all smarts can be “needy” when it comes to the battery. ED, and the HV battery can be especially sensitive towards the needs of a HEALTHY 12V.
 

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There was a computer software update that came out in late 2015 that some think might help with battery issues. Since your car was at the dealership, they should have checked and updated your software if it hadn't already been done. There is no charge for the update.

Len
 

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Discussion Starter · #4 ·
Welcome to SCoA!

What group number is your NEWLY purchased 12V?

Did the parts house confirm the new battery’s voltage as something in excess of 12.6V?

It is not uncommon for a “fresh” battery to have a dead cell or not be fully charged.

Caution, all smarts can be “needy” when it comes to the battery. ED, and the HV battery can be especially sensitive towards the needs of a HEALTHY 12V.
Hi,

I am not sure of the "group number" but I bought it from the dealership. I installed it myself because my car was dead and I couldn't get to them. Plus they wanted to charge me $500 to replace the battery.

I just tried to jump it from a jump start battery, and I guess my battery is so dead it doesn't register.

In full disclosure, I replaced the battery and then had to leave it on a trickle charger while I was out of town for three weeks. I drove it a couple of times, and then when I left it for a week, it is dead again.
 

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Discussion Starter · #5 ·
There was a computer software update that came out in late 2015 that some think might help with battery issues. Since your car was at the dealership, they should have checked and updated your software if it hadn't already been done. There is no charge for the update.

Len
Hi Len,

I will contact the dealership and check if they ran the update. I have owned the car for three years now and haven't had a single issue. It just started happening recently. Thank you!
 

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MY08 cabrio MY09 Brabus MY21 Bolt
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We may not have enough information to “virtually” diagnose?

When did this weak 12V condition begin, how long have you been using a trickle charger? What happens when you use the EVSE L1?

What period of time elapsed before getting it to “the dealership” (a M-B/ smart Center?)? Not sure that they could have done a proper test without a healthy 12V on board? How long did they have it for testing?

Something seems to be drawing the 12V down or, it’s not properly charging when on the EVSE? Shouldn’t have to have it constantly on a trickle charger…

What don’t we know? Too many questions and without pinpointing the cause, who knows?

Where are you located geographically?
 

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Discussion Starter · #7 ·
We may not have enough information to “virtually” diagnose?

When did this weak 12V condition begin, how long have you been using a trickle charger? What happens when you use the EVSE L1? What period of time elapsed before getting it to “the dealership” (a M-B/ smart Center?)?

Not sure that “the dealership” could have done a proper test without a healthy 12V on board? How long did they have it for testing? Something seems to be drawing the 12V down or, it’s not properly charging when on the EVSE? Shouldn’t have to have it constantly on a trickle charger…

What don’t we know? Too many questions and without pinpointing the cause, who knows?

Where are you located geographically?
Well, that is understandable.

Answers to your questions -

  • I don't know what the EVSE L1 is.
  • from the time of the battery dying the second time and getting it to the dealership was a couple of days
  • They had the card for several for hours. Said they tested both batteries.
  • I am in Seattle, and I can't seem to find a location, other than the Mercedes dealership, that knows anything about the car.
  • I only put it on the trickle charger because I was going to be out of town for 3 weeks

Here is the full timeline
  1. Battery first died in March/April sometime. I thought I just left something on. I had the car jumped and drove it to the store and back to make sure I charged it. The HV battery was fully charged at the time of the jump.
  2. The battery died again shortly after that. It was time for my yearly check-in, so I took it to the dealership. I did tell them that I was having issues with the 12v, and they confirmed it was not holding a charge (or something like that) and that it needed to be replaced. They wanted to charge me $500 to replace. :( A little pricy for my taste.
  3. I purchased a battery from Mercedes online and had it delivered to a dealership. In the meantime (a day or two later), my battery dies again. I was going to take it somewhere to install (Pepboys), but since the car was dead and I would need to get another jump, I decided to install it myself.
  4. The new battery is now installed, but I am leaving on vacation for 3 weeks. I leave the car with my dad on the trickle charger. He said he drove it once while I was gone. I picked up the car, drove it for about a week, never going more than a couple of days without driving it.
  5. I don't drive the car for about a week, and now it is dead again.
I guess I am trying to figure out if it is just a bad battery or if something else major is wrong. I have owned the car for 3 years and never had any issues in the past letting the car sit for a week. I even went on a two-week vacation, and it was fine.

Do ED cars have an alternator? I know very little about cars, and I am trying to avoid paying the dealership $250 per hour. I will be calling them today since they supposedly gave the car a full check over and didn't find anything else. I will also see about the battery.

Any insight you might have is really helpful. Thank you!!
 

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The EDs have a DC-to-DC convertor that performs the same function as the alternator in a combustion car.
It takes the high voltage from the main traction battery and steps it down to 12-14.5Volts to run the traditional 12V systems on the car. This convertor is energized whenever the car is on, so you can check the low voltage battery state before turning the car on, but as soon as you turn it on, it will read 14.2-ish volts because the DC-DC convertor is enabled.
 

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Still seems as though you must have a voltage draw somewhere? Have you made any changes to the car, LED bulbs or something plugged into the 12V accessory port?

EVSE (Electric Vehicle Supply Equipment) is the OEM “cable” (found in the tailgate) that connects your ED to the 120V wall outlet for charging.

As mentioned, ED has no alternator and thus must rely on the HV battery to back feed the 12V.

Jumping a dead battery for a short jaunt to the store typically would not properly charge a depleted 12V.

Unfortunately this last year+ of “house arrest” has been tough on batteries with many cars not seeing much use…
 

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Discussion Starter · #10 ·
We may not have enough information to “virtually” diagnose?

When did this weak 12V condition begin, how long have you been using a trickle charger? What happens when you use the EVSE L1?

What period of time elapsed before getting it to “the dealership” (a M-B/ smart Center?)? Not sure that they could have done a proper test without a healthy 12V on board? How long did they have it for testing?

Something seems to be drawing the 12V down or, it’s not properly charging when on the EVSE? Shouldn’t have to have it constantly on a trickle charger…

What don’t we know? Too many questions and without pinpointing the cause, who knows?

Where are you located geographically?
Still seems as though you must have a voltage draw somewhere? Have you made any changes to the car, LED bulbs or something plugged into the 12V accessory port?

EVSE (Electric Vehicle Supply Equipment) is the OEM “cable” (found in the tailgate) that connects your ED to the 120V wall outlet for charging.

As mentioned, ED has no alternator and thus must rely on the HV battery to back feed the 12V.

Jumping a dead battery for a short jaunt to the store typically would not properly charge a depleted 12V.

Unfortunately this last year+ of “house arrest” has been tough on batteries with many cars not seeing much use…
Yeah, I have been trying to keep in going at least once or twice a week because I know that sitting isn't good for the battery. The life o

Is it possible that something was disconnected while driving and/or wasn't connect back properly after my visit to the dealership?

I don't have anything connected to the 12V accessory port nor have I done anything differently with the car.
 

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Yeah, I have been trying to keep in going at least once or twice a week because I know that sitting isn't good for the battery. The life o

Is it possible that something was disconnected while driving and/or wasn't connect back properly after my visit to the dealership?

I don't have anything connected to the 12V accessory port nor have I done anything differently with the car.
First thing to do is make sure that the 12V battery has a full charge - put it on an external charger that tells you when the battery it is attached to is fully charged.

Once you have a fully charged battery you can then figure out if the battery is just bad (it won't hold a charge), is being drained by something (like a light or short), or just hadn't been fully charged and works fine.

A good 12V battery should never be dead on an ED car - the traction battery seems to maintain the 12V even when the car is off, so I am betting on a bad battery.
 

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What are you “trickle charging” with, does it rate the 12V battery condition (good/bad) and does it show voltage?

Seems that a suspect item may be the 12V charging circuit BUT, the dealer SHOULD have seen that?

12V battery is charged by the DC/DC converter stepping the traction battery down from 380V to 13.6V to power all the 12V systems like radio, headlights, power windows and such.

The 12V battery has enough juice to run the car for a couple days before it needs recharging unless there is a parasitic drain?

THEORY - You should be able test whether the DC/DC converter is working with an accessory-plug volt meter. It should rise to over 13.5V while driving. If it doesn't, then all the power for your lights, accessories, etc. are coming from the battery's stored energy which could suggest that the (expensive) converter may have issues?
 

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FYI, I bought a new battery for the car a couple weeks ago, it cost me $160 at O'Reilly's and they installed it for free.
 

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My '09 SmartForTwo's battery dies so frequently I bought one of those portable lithium ion chargers, which I have now used dozens of times. Maybe there's a short somewhere but I'm not into playing Where's Waldo.
 

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I would double down on the usual suspects, Electric Car or not: interior light not going off when the door closes, look closely at the 12V battery cables and wiggle everything to make sure they are actually tight, something plugged into the cigarette lighter, etc.. With a test meter you could determine if the battery is being drained, something any mechanic could check, once you show him where the battery is hidden.
 

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My '09 SmartForTwo's battery dies so frequently I bought one of those portable lithium ion chargers, which I have now used dozens of times. Maybe there's a short somewhere but I'm not into playing Where's Waldo.
How old is your battery? On my 2009 coupe, I am on my third battery. Original and two replacements in 12 years of ownership.
 

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I have a 2014 ED that I am on my third battery. It has a random circuit turn on that depletes the 12 V battery (found it between 3.3 V and 7 V on several occasions) and but could never catch it when I have my meter handy. It has never caused the HV battery to start discharging so far. I put a small charging harness designed for my Harley on the battery and ran an extension through the trunk and put on a 2 amp charger when I won't touch the car for two or more days. Once or twice I have found a 1-2 amp draw but it goes away before I can trace it down. I keep the interior light switched off and never put anything in the 12 V socket. I have heard of issues with the wiring harnesses chaffing in some areas and have wrapped them in electrical tape and spiral wrap to eliminate that possibility. It's no fun coming out to the car and finding it completely dead and having to rip up the passenger floor to put a big charger on the battery. I am also in a panic until I find the HV battery is still functioning. I pretty much pamper the car - it only has 9500 miles - and it still gives me grief when I come out and find it 'dead'.
 

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Discussion Starter · #18 ·
Hi everyone,

First, I really want to thank everyone for their input! This has been really helpful.

Second, I want to say that the problem is fixed. The best my mechanic (Finese) can tell is that my battery dying partially blew the fuse that connects the 12v to the HV. They reset the system and everything seems to be working now.

They also echoed @MB DNA's opinion, Smart and EV cars are very "needy" when it comes to their batteries.
 

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Hi everyone,

First, I really want to thank everyone for their input! This has been really helpful.

Second, I want to say that the problem is fixed. The best my mechanic (Finese) can tell is that my battery dying partially blew the fuse that connects the 12v to the HV. They reset the system and everything seems to be working now.

They also echoed @MB DNA's opinion, Smart and EV cars are very "needy" when it comes to their batteries.
By the way, if you are storing the car for an extended time period, the best thing to do is to disconnect the negative terminal of the battery - after you confirm the car is operating correctly.
 
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