Smart ED dead traction battery restoration
We live in Central Oregon ... beautiful high desert country ... from which this winter, we escaped. We left our 2013 Smart car in the garage, and connected to a Siemens Level 2 charger, thinking all would be well when we returned in the spring. Unfortunately, when we returned we found the car to be completely dead, even though the external charger said it was connected properly, and that the car was fully charged ... or at least showed green lights all around.
I found the regular 12V battery in the car to be dead, and charged it with an external automotive charger. The car then looked pretty much normal ... except the traction battery indicated zero charge, and there was a flashing dashboard warning stating that the car required service.
Not all Mercedes dealerships are authorized to work on the Smart Electrics so my choices were either downtown Portland or Medford. Not wanting to fight Portland's downtown traffic with a loaded trailer, I contacted the Medford folks and arranged for a service visit at their next available opening. The following week I loaded the car onto a trailer & made the 3-hour trip (each way) south. I'd already explained the situation to the service advisor on the phone, but had to go through the whole thing again when I got there ... telling them again about the extended storage of the car, and that afterwards, the main battery wouldn't take a charge from a Level 2 charger (or the 110V charger supplied with the car). I specifically requested a thorough inspection of the battery, on-board charger, and battery management system. I authorized 3 hours of shop time for these tasks. Even though I'd scheduled this service a week in advance, I had to leave the car at the dealership as the service tech certified to do this work was surprisingly not on site for the scheduled service.
A week later I was contacted by the dealership and told, "The traction battery will not take a charge, and needs to be replaced." I asked how they had attempted to charge the battery and was told that they'd used a Level 2 charger ... the same kind I have at home ... and that their test indicated that several cells in the battery pack were well below minimums. They could not provide a list of which cells were bad. I asked if they'd tested the on-board charger and BMS, and they said no, but their service procedure indicated that the traction battery needed to be replaced, and that's all they were authorized to do. I was quoted a replacement price for the battery of $9000 ... and that price did not include installation ... and a delivery time of 6-8 weeks. I asked how they could be certain that a battery replacement would cure the issues exhibited by the car if they hadn't tested the BMS and on-board charger, and the service advisor told me that replacing the battery was the procedure they were required to follow.
I returned to the dealership, found that I'd only been charged for one hour of "service," paid the $160 charge, and trailered the car home. And by the way, loading a dead car onto a trailer by yourself is never any fun. (They were prohibited from helping me, according to their service manager, and I thanked them for the clarity of their procedures. Silently.)
In 2013, we'd been told by the Mercedes dealership where we'd purchased the car that the battery pack and drive train in this car were actually a Tesla system, and because the Tesla/Panasonic 18650 batteries and modules containing them are now available, I decided to try to repair the car myself. I removed the battery pack and opened it ... and soon determined that the batteries inside were not Tesla/Panasonic cells, but Li-tech pouch cells and that the whole assembly was manufactured by SB LiMotive, a German joint company of Bosch and Samsung SDI. I've also discovered that SB LiMotive is now defunct. These discoveries have dampened my enthusiasm for attempting a repair myself, and I still have a nagging suspicion that because the car was working perfectly when we parked it and was dead when we next tried to drive it, some other part in the car has failed, making any repair or replacement of the battery a fools errand ... especially when the Mercedes folks seem unwilling or unable to complete this work.
But still game, I measured the voltage of each of the 3 modules inside this battery pack, and all were about 13.5V ... or about 10% of what they should be. I attached a lab power supply to each of the modules in turn, and, as this power supply was only capable of delivering a controlled maximum of 35VDC, I slowly brought each module to that level, bringing the total pack voltage to 115VDC ... or about a third of what it should normally be. I saw no current spikes during this charging, and noticed no unusual smells or sounds.
With a little more disassembly, I discovered that I could measure and charge individual cells without disassembling the modules, and did so with 4 cells in one of the modules. These cells measured between .8 and 1.8 VDC before any charging, and by ramping up the charging voltage on each of the cells to 4VDC very slowly, I've managed to revive these cells. I started the charging at 100mA on one of the cells, and it took about 12 hours to get the voltage to 4VDC. On the last cell I experimented with, I held the charging current maximum to 1A, and it tapered much more rapidly as the cell voltage neared 4VDC. 24 hours after this charging procedure, all of these cells measured about the same value: 3.7VDC.
These results are encouraging, but I still had no explanation as to how the battery could have been so completely discharged while plugged in to a certified charging system. I later learned that if the key wasn't left in the ON position the 12V battery would soon run down, and that this would then interrupt the whole charging and temperature control system. Because the car was parked and connected to the charger in a garage where the ambient temperature was below freezing for more than 2 weeks, I worried that the cells in the traction battery may have been damaged by freezing. Or the Siemens charger just fried the whole battery pack. Or it could be that the BMS in each module is taking far more energy than it should ... or the maybe the phase of the moon was just wrong. I just didn't know.
Resolute, I continued charging individual groups of cells until all cells in all modules retained 3.7VDC for at least 24 hours, and each module looked pretty much like the one in the attached photo.
This brought the total unloaded voltage of the traction battery pack to 337.6VDC, which is very close to the nominal, unloaded voltage of this pack of 339VDC. I reassembled the battery pack, sealed it, and reinstalled it in the car.
When I turned the key, the results were disappointing. The dash energy displays still both read zero, and there was a red flashing notification on the dash that the traction battery had a fault, and that the car should not be towed. Subsequently, I've learned that "only the dealer" can reset a traction battery fault indication ... and this must be done before the car can be driven ... and since the dealership in Medford will certainly refuse to do this, I'm wondering if there is an alternative?
Any and all help would be appreciated.