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Discussion Starter · #1 ·
I'm about to leave my 2019 Fortwo in storage, unattended for about 4 months. From what I've read, I shouldn't be worried about flat spots in the tires due to the light weight of the vehicle. I've read conflicting reports on what to do re the two batteries, however. Some folks suggest fully charging prior to long term storage, some suggest only charging to 40 or 50%. With respect to the 12 volt battery, some recommend using a smart charger to keep it maintained, others suggest simply disconnecting the GND until I return. Any suggestions or recommendations? Thanks.
 

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"Some folks suggest fully charging prior to long term storage, some suggest only charging to 40 or 50%" I would just leave it connected to the level 1 charger cable while you are gone, as recommended in the owners manual (p. 63 on my 2017 manual). When the charger is running, it is also supplying 13.6 volts to the 12v. battery. You also have to be sure the car doesn't exceed the high temperature limit, again the charger cable will be there to charge up the battery as it cools itself. The m/b dealership who has to honor your 4 yr. warranty might have the best advise, if you can get a response out of them. Definitely don't want to void the warranty if something goes wrong.
 

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Discussion Starter · #3 ·
"Some folks suggest fully charging prior to long term storage, some suggest only charging to 40 or 50%" I would just leave it connected to the level 1 charger cable while you are gone, as recommended in the owners manual (p. 63 on my 2017 manual). When the charger is running, it is also supplying 13.6 volts to the 12v. battery. You also have to be sure the car doesn't exceed the high temperature limit, again the charger cable will be there to charge up the battery as it cools itself. The m/b dealership who has to honor your 4 yr. warranty might have the best advise, if you can get a response out of them. Definitely don't want to void the warranty if something goes wrong.
Thanks. I hadn't seen that in the manual. In my 2019 manual the relevant passage is on pg 72 and it states, under the section titled "Battery Care" to "Connect the vehicle to a power supply when parking it for an extended period of time." The manual also states, on page 71 "If possible only charge the high-voltage battery when the charge is below 80%."
 

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Yeah, it does a better job of charging, from what I understand, if you can just drive the car until the battery is down the 40% soc, and it can somehow give you a better range indication of it's capability. All the EV's (from tesla to leafs) really don't want you topping off when you are 80% or above (just like cell phones), and some manufacturers go so far as recommending you stop charging at 80% unless you are planning a big trip and need all the capability. My wife's 2020 Hyundai Kona EV gives the options to stop the charger at 80, 90, or 100%. Smart hasn't stated that in our model years manual, but they may wish they had. And since they stopped selling them here, I have no idea what they state now in the newer manuals. Guess the Euro and GB forums might have some more insight, but I haven't investigated.

But if you're leaving for 4 months, the best you can do is plug it in and leave it plugged in at 100%. That way if it needs more juice, it can just turn on and recharge. Hopefully you have to someone check on it if there's a power outage while you are gone, in case a breaker gets flipped. If you have read much on the forum, you are probably aware that the 451's can "brick" quite readily if the 12v battery fails and the bms decides to go into shutdown mode. So far I have found no post of the same happening to our 453's.
 

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Discussion Starter · #5 ·
FYI. Just found this on an earlier thread in this forum from about two yeasr ago from Yinzer:


This forum has accumulated enough case studies of high voltage (HV) battery failure if the 12V battery is left dead for more than several days that the following warning is now warranted!

1. Through a defect or design feature in the Smart ED that is not entirely clear, it is now almost certain that if the 12V battery is removed or becomes discharged, and is allowed to stay discharged or removed from the vehicle for an uncertain period of time (on the order of several days to a month) the HV battery will also then totally discharge itself over an unknown time period (probably several days) and be ruined - resulting in a likely total write-off of the car.

2. To prevent this from happening, any Smart ED owner who plans on not operating their ED for 2 weeks or more MUST connect a maintenance charger to the car's 12V battery and double-check the charger's proper operation. IMPORTANT NOTE: Keeping the car connected to a charging station or the car's wall socket charging adapter is NOT, repeat NOT a substitute for this measure. It will NOT keep the 12V battery charged!

3. Consider running a pair of charging wires (16 gauge or so) from the 12V battery terminals to an appropriate location under the service flap for easy 12V battery charging.

4. Connecting the car to charging station is only needed of the car will be subject to temperatures lower than -20C (-4F) or above 40C (104F) otherwise, it is best to store the car with the HV pack at an indicated state of charge of 80 percent. But ALWAYS keep a 12V charger connected to the 12V battery.
 

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Yes, this is true for the 451's (2012-2016) which are ED3 models, but the 453's (2017-present), are ED4 models. These do not have this problem. If I had a 451 I would do what Yinzer says. But not for the 453. I would just plug it in and let it be. Like the manual says.
 

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Discussion Starter · #7 ·
Yes, this is true for the 451's (2012-2016) which are ED3 models, but the 453's (2017-present), are ED4 models. These do not have this problem. If I had a 451 I would do what Yinzer says. But not for the 453. I would just plug it in and let it be. Like the manual says.
Took your advice and double checked with the dealer that sold us the car. They confirmed that the car should be plugged in. They further added that I should not use our Level 2 charger, only the Level 1 charger cable that came with the car. Somewhat surprisingly, slightly contradicting the manual, they recommended strongly that I should keep the car plugged in if I'm not planning on driving the car for even a few days. Thanks for all your help.
 

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Discussion Starter · #8 ·
Well...the plot thickens. Last night when I checked my main battery was at 80% but I hadn't driven the car for a couple of days. I pulled out the 120V charging cable and, per the dealer's recommendation, I plugged it in and the LEDs indicated it was charging. Fast forward to an hour ago. The charger LEDs are off (except for the power indicator), I unplug it, open the door and the car is completely dead. I check the battery with a voltage meter and it shows about 2 V. I just plugged in into a maintenance charger (NocoGenius 2D) and have my fingers crossed.
 

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Took your advice and double checked with the dealer that sold us the car. They confirmed that the car should be plugged in. They further added that I should not use our Level 2 charger, only the Level 1 charger cable that came with the car.
Curious, THE DEALER is a prior smart Center (M-B Dealer)?

Sounds like this could be a LONG agonizing 4 months? Are you in an area prone to weather or grid related outages?

Any friends or family who might be able to check on things every couple weeks?
 

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How old is the 12v battery? The car should supply over 13.5volts to the 12v battery when the charging starts. The car should have also told you the time when it expected the charge to be completed, not just the LEDs in the plug port. (Sometimes I have to open and close the door to get it on the dash screen.)
 

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Discussion Starter · #11 ·
How old is the 12v battery? The car should supply over 13.5volts to the 12v battery when the charging starts. The car should have also told you the time when it expected the charge to be completed, not just the LEDs in the plug port. (Sometimes I have to open and close the door to get it on the dash screen.)
THE DEALER is a prior smart Centet (MB Dealer). In fact, the dealerships where we bought the car two years ago. The battery is only three months old. It was replaced by the dealership when the car went "dark" the first time. The car was at 80% charge when I plugged it in yesterday. This is all quite frustrating. According to the Noco the battery has still not reached 50% after having been charging for about 12 hours.
 

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If it's only 3 months old it should still be under warranty. It should be a 60 amp hour enhanced flooded battery, m/b p/n 453 982 0200. This should be readable, though possible upside down, right on the battery. If you have the 451 p/n, it's the wrong battery for your car. I don't think a battery can be recovered reliably when it is down to 2 volts, despite what your charger may say it can do.

IF you left the car lights on, then there will be a battery drain on your system. I found this on Xentry tips 01-31-2018:
Complaint: 12 V battery discharged - Vehicle does not start ONLY affects 453 smart electric vehicles!! Cause: If the customer fails to turn off the vehicle's lights by leaving the rotary light switch left in the "ON" position, the in-vehicle CAN network will not go in to an idle state. Even though after five minutes in the "ON" position the lights turn off automatically, the CAN network will remain awake creating a high quiescent current draw and cause the 12 V battery to discharge. Remedy: Remind the customer never to leave their vehicle lights in the "ON" position when exiting the vehicle. The customer should use the "Auto" position instead of the "ON" position. A solution in the form of new software is currently in development that will help prevent battery discharge if the customer leaves the lights on after exiting the vehicle. Until the new software is released, please follow Xentry for proper 12 volt electrical system and 12 volt battery diagnosis.
 

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THE DEALER is a prior smart Centet (MB Dealer). In fact, the dealerships where we bought the car two years ago. The battery is only three months old. It was replaced by the dealership when the car went "dark" the first time. The car was at 80% charge when I plugged it in yesterday. This is all quite frustrating. According to the Noco the battery has still not reached 50% after having been charging for about 12 hours.
Something doesn’t seem right…

Your MY19 smart going “dark” three months ago requiring that M-B replace the 12V is at best worrisome.

You should still be under Factory Warranty, have them flat tow it in for warranty repair.
 

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Discussion Starter · #15 ·
I agree. I'm just less than optimistic. We live about 100 miles from the dealership. Their "understanding" is that they are at most obligated to tow it from my house to the dealership and that I am responsible to getting it back to my house, even though the car only has a range of 60-70 miles. Last time it took multiple calls to MB to get them to "cover" the cost of towing back to my house, and MB was quite clear that this was a one-off.
 

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Discussion Starter · #16 ·
Update. The dealer said I should jump start the car. I did and the car started right up. After driving for about 30 minutes the voltage on the battery was up to 11 volts from under 2 volts. I left it plugged in all night and, when unplugged, it was at just over 11 volts. It's now on a battery maintainer (2 amp) and, after 5 hours is reading just under 12 volts, although the diagnostic LEDS show that it is still at less than 75%. Fingers crossed.
 

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Yeah, it does a better job of charging, from what I understand, if you can just drive the car until the battery is down the 40% soc, and it can somehow give you a better range indication of it's capability. All the EV's (from tesla to leafs) really don't want you topping off when you are 80% or above (just like cell phones), and some manufacturers go so far as recommending you stop charging at 80% unless you are planning a big trip and need all the capability. My wife's 2020 Hyundai Kona EV gives the options to stop the charger at 80, 90, or 100%. Smart hasn't stated that in our model years manual, but they may wish they had. And since they stopped selling them here, I have no idea what they state now in the newer manuals. Guess the Euro and GB forums might have some more insight, but I haven't investigated.

But if you're leaving for 4 months, the best you can do is plug it in and leave it plugged in at 100%. That way if it needs more juice, it can just turn on and recharge. Hopefully you have to someone check on it if there's a power outage while you are gone, in case a breaker gets flipped. If you have read much on the forum, you are probably aware that the 451's can "brick" quite readily if the 12v battery fails and the bms decides to go into shutdown mode. So far I have found no post of the same happening to our 453's.
I have heard of at least one case of a 451 that was kept plugged in for charging over a long storage period and it bricked when the 12V battery died anyway. Experiments I have run indicates that charging (both traction and 12V battery) only turns on if the SOC falls below 90 or 95 percent.

It is well known that all lithium ion cells don't like storage at full SOC - it contributes to "calender degradation" - degradation that happens even without discharge/charge cycles. This is especially significant at warm temperatures. So I would only only keep it plugged in for charging if it is being stored outside in winter and is subject to temperatures below -25C. Otherwise, I would store it at 60% to 70% SOC and disconnect the negative 12V battery terminal.
 

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Update. The dealer said I should jump start the car. I did and the car started right up. After driving for about 30 minutes the voltage on the battery was up to 11 volts from under 2 volts. I left it plugged in all night and, when unplugged, it was at just over 11 volts. It's now on a battery maintainer (2 amp) and, after 5 hours is reading just under 12 volts, although the diagnostic LEDS show that it is still at less than 75%. Fingers crossed.
If the 12V battery was allowed to discharge to 2V you should consider it to be bad and replace the 12V battery. And a 12V lead-adic battery that is still below 12 volts after all that charging is definitely bad.
 

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Discussion Starter · #19 ·
Well...according the Noco, the 12V battery is slowly coming back to life. It is now pulsating green (> 75%) and the multimeter has been reading a solid 13V for the past 24 hours. I understand your concerns, but I'm remaining hopeful for the moment given these results, combined with the dealer being quite adamant that a 453 should be plugged in via the supplied 120V cable for extended storage. I've read that it can actually take weeks sometimes to desulfate a battery. So again, cautiously optimistic.
 

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Well...according the Noco, the 12V battery is slowly coming back to life. It is now pulsating green (> 75%) and the multimeter has been reading a solid 13V for the past 24 hours. I understand your concerns, but I'm remaining hopeful for the moment given these results, combined with the dealer being quite adamant that a 453 should be plugged in via the supplied 120V cable for extended storage. I've read that it can actually take weeks sometimes to desulfate a battery. So again, cautiously optimistic.
If you are in the USA, it is highly likely that your Mercedes Benz dealer knows f--- all (to use an expression from across the pond) about what is actually good for the car. I had to show the service rep at my dealer how to "start" the car. And while I don't know about the 453 manual, there is information in the 451 manual that is simply wrong. Also, regarding lead acid batteries, this "desulfation" stuff is largely foo-foo. But if the bug in the 451 has really been fixed in the 453, then there is no harm in letting the 12V battery go dead anyway during storage.
 
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