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Discussion Starter #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
 

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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.
 

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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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Discussion Starter #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
 

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Discussion Starter #6
Why would you want to "routinely" replace the 12v battery.....? :shrug:
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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Wouldn't it be easier (not to mention cheaper) to just put a trickle charger on the 12v if the car is not going to be used for this unknown period? :)
 

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Discussion Starter #8
Wouldn't it be easier (not to mention cheaper) to just put a trickle charger on the 12v if the car is not going to be used for this unknown period? :)
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
 

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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.
 

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I just bought a 12v socket expander that has a volt meter built into the plug. It usually reads 13.8v or so when the car is running.
 

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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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Vincent,

You can always make sure the 12V battery is fully charged by just turning the key switch on and leaving it on for 10 minutes of so.

Paul D.
 

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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
 

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I am reading your comments, I am also worry if the 12v battery goes wrong and damages the HV battery.
While nobody is sure, the 2016 software update may prevent these consequences of a drained 12V battery - and it may also prevent the 12V battery from discharging too (by programing the syatem to periodically turn on the DC-DC converter to charge the battery. Make sure that is done if you have not done so. It should be free to have it done.

Replacing the 12V battery is easy. Just follow the usual precautions. The number one rule is to always disconnect the negative terminal first to prevent accidental shorts with the wrench to the cars frame.
 

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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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Is there a way to check the software version yourself? Or can only the dealer tell you which version you have?
 

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Discussion Starter #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
 

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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.
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
 

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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
Couple things:

1. There should be no "hopefully" about the service they did on your Smart (especially for $540) you should have gotten a detailed statement on the work they did including the service campaign software update.

2. Since the cigarette lighter is only on when the car and the DC-DC converter (equivalent to the alternator in a IC engine car) is on, that 14.5 volts reading tells you nothing about the health of the battery. You need to check the voltage of the battery when the keyswitch is off. It should be at least 12.5 volts or so.
 
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