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Replace 12v battery routinely?

8K views 43 replies 14 participants last post by  VSAncona 
#1 ·
On my ICE cars I have never replaced a battery until it started having symptoms. Sometimes I'd go 10+ years with the same battery.

But do I need to change my thinking with the 12v battery in the EV's? We've got a couple of threads going now where leaving a dead 12v battery in the car might "brick" the HV battery and even though the HV battery might still be functional, there is no way anyone has come up with yet to put it back in service.

The 12v batteries on my two Smarts are each about five years old and reading 12.7v. I think they are both the originals, but here is an interesting note in the service record I got from the dealer before I bought the coupe.

"Radio left on by sales. Battery drained and had to be charged. Okay after charge."

Apparently that situation had no bearing on the HV battery.

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 12,000 miles
 
#2 ·
My 12V battery went bad around the 4 year point. Symptoms were that starting the car became unreliable over a period of a week or two. In my case, I had enough indication of a problem that I was eventually able remove the 12V battery, have it tested, buy a replacement, and get it installed, all in one afternoon. One of the cells in the 12v battery had gone bad so it was only holding around 10v.

I donÂ’t know what the timeline is for HV failure but it seems an afternoon with no 12V battery installed didnÂ’t do any harm.

Knowing what I know now, I would have put the car on a trickle charger or jumpered the car to a good 12v battery for the afternoon.
 
#3 ·
My 2016 ED was built ~5/2015 so battery is now at least 4 years old if it is still the original. Time to check it out! Are there any clues if it is factory brand or country of origin? If it was replaced at some point in North America it might have a familiar brand name and maybe the sticker where you pop out the install date.
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#4 ·
I just serviced my cabriolet and checked the 12v battery. it is very clearly marked with a Smart sticker and part number. I tried to find a date of mfg. or in service, but nothing was visible and I wasn't curious enough to want to remove it to check.

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 12,000 miles
 
#6 ·
Because of a dead 12v causing the HV battery to become a brick after a period of time. That period of time has not been determined, but it could be only a matter of weeks, maybe less?

Read the first sticky in the electric car forum for the warnings.

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 12,000 miles
 
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#8 ·
Yes to both questions, but we all need to make choices. What do you feel most comfortable doing? The way I use my two, I don't foresee ever letting them sit unused for a long period of time, but what happens if life gets in the way and something unforeseen pops up?

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 12,000 miles
 
#9 ·
A 12 volt car batteries, average life is 4-5 years. ICE, EV. I have a 7-70,000 mile battery, in one of my vehicle. It’s still going strong. After 6 years.

Test the strength of your battery, while your EV is running. It should read 14.5 volts. Your going to need a passenger to help out.
 
#13 ·
A 12 volt car batteries, average life is 4-5 years. ICE, EV. I have a 7-70,000 mile battery, in one of my vehicle. It’s still going strong. After 6 years.

Test the strength of your battery, while your EV is running. It should read 14.5 volts. Your going to need a passenger to help out.
I am reading your comments, I am also worry if the 12v battery goes wrong and damages the HV battery.
With the Rob22304's idea to buy a 12v socket expander that has a volt meter built into the plug, this kind of thing will be perfect to have on the Fortwo's glovebox? right? it's good and reliable?
62285

Also I am wondering, to change the 12v battery when it's bad, it's not difficult? not extra precaution to do? (I did before on gas car)

Thank you
 
#11 ·
Both my island EVs suffered from the short 2.6 mile each way trips to the ferry and both were in the low 90 percentile of charge. So I charged them up to full and decided to take the long way home from the ferry at least until I could come up with solutions. The Spark_EV has the 12v battery right up top under the hood so this is very easy to give a weekly boost. The Smart_ED has the 12v battery hidden under the passenger foot panel so I figure a plug could be mounted under the dash and the door will be adjar during the periodic charging.

I've plugged in voltmeters designed for the cigar lighter socket in both cars but of course these disconnect as soon as you shut down the system. But look at the indicated voltage as soon as you turn on the car: if it is 12.6v or less then that would indicate a stress situation ie dc/dc converter has not had sufficient time to fully maintain the 12v battery. If it jumps to 14v immediately then you are ok for the time being.

Now not many owners are only driving 2.6 miles at a time like me so the engineering of these two EVs cannot really be faulted. But it has been enlightening to discover where the margin exists! Btw both cars are equipped with AGM original batteries (OEM) and if they ever need replacing be sure to pay the extra for the AGMs.
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#15 ·
Are you guys sure the 12V-thing for the cigaret lighter is worth it? The cigaret lighter is only activated, when the DCDC-converter is keeping the 12V circuit at about 14V. So it's never showing the voltage of the 12V-battery.
 
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#19 ·
Thank you Yinzer for your answer, I appreciate. Now I need to find a way to figure it out the software version.
I just went to MB, (FYI it cost me $540 for the 40k/4y service) hopefully they did it.

For the 12V thing for the cigaret lighter, I doesn't matter, if it shows around 14.5V while it's running, we are good, right?

Thank you
 
#17 ·
You got a couple of options. If you have one of our battery test units, we can tell you from the data it spits out. However, probably the best way is to contact a Smart dealer or any cooperating Mercedes dealer, give them your VIN and they can pull up your car's VMI to see if there are any outstanding service programs that haven't been applied. It's unlikely, but there may be more than the one you're asking about.

Len
 
#31 · (Edited)
I routed a pair of voltage check and charging wires from the terminals to under the service flap. An existing rubber wire harness gland near the steering column can be used to route the wires through the "firewall". The battery charging wires could prove invaluable if you find the battery dead with the car locked. The "manual" key lock on the driver's door is not actually a mechanical lock - it actuates a (battery dependent) switch(!).
 
#32 ·
On my ICE cars I have never replaced a battery until it started having symptoms. Sometimes I'd go 10+ years with the same battery.

But do I need to change my thinking with the 12v battery in the EV's? We've got a couple of threads going now where leaving a dead 12v battery in the car might "brick" the HV battery and even though the HV battery might still be functional, there is no way anyone has come up with yet to put it back in service.

The 12v batteries on my two Smarts are each about five years old and reading 12.7v. I think they are both the originals, but here is an interesting note in the service record I got from the dealer before I bought the coupe.

"Radio left on by sales. Battery drained and had to be charged. Okay after charge."

Apparently that situation had no bearing on the HV battery.

Len
2014 EV Coupe 18,000 miles
2014 EV Cabriolet 12,000 miles
Okay, going back to my original post that started this thread. We now have two or three more cars where the HV battery is bricked or heading that way. Not sure if the battery update program that came out several years ago fixed this issue. Both of my cars have had the update. Unknown whether the cars "bricking" had the update or not.

So back to my original question. Is it wise to change the 12v battery after five or six years when there is no sign of a problem or do you wait for the 12v battery to give it up? I'm leaning to routine replacements.

Len
2014 EV Coupe 19,500 miles
2014 EV Cabriolet 17,000 miles
 
#33 ·
My '09 is a gasser, so this may not apply. Since the battery in the 451 is not very accessible, I routinely change it about every four years. After the original, I have done two replacements and will be due again in a little over one more year. Maybe excessive, but I like the peace of mind.
 
#34 ·
Thanks for your reply. If you lived closer, I'd take your four year old batteries and use them for several more years. :) Just kidding - we each need to do what makes us feel comfortable. Gas and diesels I drive until the battery tells me it's over, but there is no real downside to doing that. In the electrics though there seems to be a connection between the 12v battery going bad causing the $10,000 HV battery to brick itself. I think I may have convinced myself.

Len
2014 EV Coupe 19,500 miles
2014 EV Cabriolet 17,000 miles
 
#35 ·
Thanks for your reply. If you lived closer, I'd take your four year old batteries and use them for several more years. :) Just kidding - we each need to do what makes us feel comfortable. Gas and diesels I drive until the battery tells me it's over, but there is no real downside to doing that. In the electrics though there seems to be a connection between the 12v battery going bad causing the $10,000 HV battery to brick itself. I think I may have convinced myself.
I am wondering also...I waited potential answer, I liked the idea of the update saved everything and didn't brick the battery... but if it's not true... My only idea is to keep an eye with the voltmeter weekly on the battery and check the voltage (I am handy, but I don't know anything about EVs...). What I know is my battery is from 2014 (never changed) and I should worry...
 
#36 ·
Yeah, I'm due to service my coupe this spring and I'm leaning to just going ahead and replacing the original 12v battery. In these cars I guess maybe I need to think differently unless more info comes out about the update which I have had done on both of mine.

Len
2014 EV Coupe 19,500 miles
2014 EV Cabriolet 17,000 miles
 
#37 · (Edited)
Car been sitting for a few days. Today cigar/voltmeter says: 12.0v . . 11.8v . . . 14.2v. Not good, time for direct action so hooked up tiny float charger thru passenger window. With luck this will maintain slowly dying 12v batt during my absence for a couple weeks.

63770



I had two different little float chargers on hand, both from Harbor Freight I believe. One has the usual long cord from the wall-wart to the device and its short clip leads. The other has only short leads; get the long leads. As seen above the 120vac plug/wall-wart is inside a juice bottle held onto the door handle with a hole punched & twistums. The 12v thin wires fit when window almost fully closed, still loose. So only low voltage inside car and the wind can't blow away.
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#40 ·
I purchased a 2014 ED last December. It currently has around 30,000 miles. I’ve been reading a few threads like this one that talks about the 12v battery failing and bricking the HV battery. So today I decided to take a look my battery and it appears to be the original battery, with a date of 10/2014.

So now I have a couple of questions. As long as I replace it right away (within a day or two) is it okay just to wait until this battery dies? Or does it need to be replaced before it reaches that point?

Second question is how can I tell if my car has had the battery software update?
 
#43 ·
Second question is how can I tell if my car has had the battery software update?
The battery test unit that you bought will report the firmware date of the battery management system. We have strong empirical evidence (from testing one of sokoloff's cars before and after getting the software update) that the software update changes this version field and therefore you can very likely rely on that output from the test results to tell you if you if the software update was applied to your car if you can't get definitive information from a dealer.

There will be three lines in the report that tell you the production date, the factory acceptance test (installation) date, and the software revision date.
Here's an example from another user who had a battery replacement in 2019 (so showing the most recent battery software version date):
Code:
Battery Production [Y/M/D]: 2019/6/11
Battery-FAT date   [Y/M/D]: 2019/6/12
Rev.[Y/WK/PL] HW:2014/34/0, SW:2014/18/0
Two of the older software revisions that we've seen are:
Code:
Rev.[Y/WK/PL] HW:2012/38/0, SW:2012/35/1
Code:
Rev.[Y/WK/PL] HW:2013/29/0, SW:2013/29/1
Sokoloff's car was upgraded from 2013/29/1 to 2014/18/0 during the service bulletin application last summer.
 
#41 ·
Couple of suggestions for you. Use a multimeter to check the voltage of your 12v battery. If it's 12.4v or so and up, you should be fine for awhile. If you don't have a multimeter, borrow one or maybe the McParts stores offer to check your battery for you for free. If you go the McParts store route, it would probably be advisable to make the battery accessible by removing the carpeting and the Styrofoam. There are a couple of fasteners that the McParts store guys might just ignore and try to Conan the thing out. The test unit you are getting will also allow you to test your 12v battery. I would not wait until the 12v battery dies before replacing it. That might be okay with an ICE, but the EV is a whole different story and concern.

On the service program update, any Mercedes dealer should be able to tell you if your car has had that done as long as they have your VIN. If your dealer is a PIA about checking it for you, you can call or e-mail a cooperating dealer like the Mercedes dealer in Cary, NC. They have been very helpful.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 
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