The early builds had an especially long transit time, I know at one point shipping was halted to fix an issue. A lot of the early cars had 12v issues, I was thinking they did a software update to address it.
That DC-DC feature operates like the alternatoe or generator in an ICE car. The 12V battery is constantly under light loads, even when the car is asleep. The DC-DC charging system is supposed to replenish the 12V battery under those conditions. Early builds had a sfotware issue that allowed the 12V battery to completely discharge while the vehicle was asleep. There was a software patch for that.I just checked the owners manual online and it says that the high voltage battery will charge the 12v battery if necessary. So no need to charge the battery manually as far as I understand.
The (easier) alternative is to turn on your Mach-e, disable the auto-off setting, and let it sit in in Park for a couple hours 'on'. The onboard dc-dc will come up to it's operating voltage, and top up the 12v battery all by itself.
This won't work completely. Desulfation of an AGM is a time-limited process, so only a couple hours won't do it. The charging voltage needs to be applied for at least 24 hours continuous. In my test case with a mildly sulfated battery it took 3+ days to see the current decay to what I would consider a "full desulfated" level. You could still potentially do this with your car, but I don't recommend people leaving their car on unattended for days at a time because of the security risks, and it's sort of a waste of electricity (5-10 kWh) on idle currents.
Yes, with a normal healthy battery the charging system will keep it in decent shape with no extra charging needed. But with a sulfated battery the charging system won't run long enough to clear all of it out, and capacity will be degraded. Because your car was sitting for so many months, it probably has some sulfation buildup in it. Early builds also had the 12V charging software issues. In your case I'd recommend you take it to the dealer for the TSB software updates first if you haven't yet. Then I'd recommend leaving it on a battery charger for a week because the sulfation is almost a year old and is likely very hardened by now. If you get the message again after doing those two steps, then you probably need a new battery.I just checked the owners manual online and it says that the high voltage battery will charge the 12v battery if necessary. So no need to charge the battery manually as far as I understand.
Thanks for the advice. I will go ahead and charge the battery as you suggest.
Well, the 12V Fault message popped up again this morning, so I guess a visit to the dealer is in my future. I guess I'll wait until after 11/15 so I can have the glass recalls done at the same time.
I’m curious, when the NOCO goes into maintenance mode, does it shut off the output? The charger needs to output 13.6V+ continuously in its final mode for the desulfation to work. Otherwise you only got 7 hours of charging instead of 48. The manual isn’t really clear on what the charger is actually doing in those modes. Maybe some of these new “smart” chargers won’t work because of power saving modes I didn’t consider. If somebody could check the voltage after it’s been in the final mode 12+ hours then we’ll know.
My interpretation of the manual is that yes, it shuts off the output when in maintenance mode and just monitors the battery. In this mode, it will switch back into optimization mode as needed to keep the battery healthy. I'd love to be able to test this, but I'm not sure how to test the output of the charger when in this mode since it has to be connected to the battery.
Just use a voltmeter on the + and - jump terminals with the charger connected to check the voltage. If the charger is off the battery voltage will decay to less than 13.3V. If charger is staying on float mode it should keep it at 13.4V+.
Correct, only if the battery is healthy to begin with and the software is up to date. I'm offering this advice to help people fix their marginal batteries themselves to avoid replacement. Some people have reported a 1-month wait on replacement 12V batteries right now, and going to the dealer and being without your car is a hassle. You're certainly free to go to the dealer and wait for a new battery if you want, but some people would rather try the charging routine first to see if that's really necessary. It doesn't hurt anything to try, choose your own path.
Our vehicles are less than 1 year old... if there is a problem with either battery, or on-board charging modules it is best to get it in process and squared away thru Dealership under warranty. No need to mess with extra expense and trauma if there is something wrong with on-board that needs to be fixed!
