12v battery - difference between charging and maintaining?

[Bullitt_&_MME]

The low range is why your 12V battery was not charged. I believe once the HVB goes below a certain level, it won't run the DC-DC converter any longer to try and keep the 12V charged up.

Your 12V may be fine, if you are able to charge it externally, and then get on a L2 charger for the HVB.

Your dealer delivered the car to you in this condition?

no - they didn't deliver it to me. It's here and they called me w/ the "bad news" and immediately blamed the 12v as "dead" when in reality I knew it could be any number of other complications.

As we speak it's hooked up to a 12v charger, as well as level-2 wall charger.

Sponsored

 

[Mach-Lee]

yep my GT just arrived dead today. Anything else to do out there besides charging the heck out of the 12V and charging the MME up to it's highest levels too?

Mine arrived today w/ a dead 12v and <17 miles left on the range...

Yikes! Why am I not surprised nobody could be bothered to charge it up anywhere in the process...

The car probably gives up trying to recharge the 12V battery when the main battery gets down to 10-20%.

Yes, you will need to charge the 12V for a while to try to bring it back. More details here if you're interested: How to Recondition/Service Your 12V Battery

 

[Bullitt_&_MME]

Yikes! Why am I not surprised nobody could be bothered to charge it up anywhere in the process...

The car probably gives up trying to recharge the 12V battery when the main battery gets down to 10-20%.

Yes, you will need to charge the 12V for a while to try to bring it back. More details here if you're interested: How to Recondition/Service Your 12V Battery

Thank you! Yes, the main batteries for the drivetrain had ~17 miles left on the GOM - so I think between the two, the car was basically DOA.

Both the wall charger and the 12V charger were put on the car ~130pm yesterday and left alone. My sales guy should be calling me this morning with the news on whether the car will turn on or not.

 

[Smuddell]

To save energy, the system voltage may only be held around 13.2-13.8V to maintain the battery rather than charge it. This is why you'll notice the battery isn't fully charged, or see the messages regarding it. When the BMS thinks the battery is too low, it will switch to a higher voltage in the 14-15V range to actually charge up the battery to a higher SoC. Again, this is done to save energy and also prolong the life of the AGM. Seems like the Ford BMS targets about 70-80% SoC on the 12V batteries from what I've seen.

Fully charging your 12V battery overnight after delivery isn't a bad idea, I'd recommend that as well. It's probably been sitting at a low SoC for a while during transport, and probably has some internal sulfation built up. Putting it on an AGM charger and letting it maintain for 24-48 hours should mostly clear that up and restore most of the capacity.

But once you've fully charged the battery per the above, it should take care of itself. If it gets low or dies again, the battery is bad or the car has a software issue that should be corrected. A marginal battery will cause some issues due to the lack of capacity. It needs to power modules for long enough in between DC/DC wakeup events during certain conditions like sleep. Trickle charging is just a Band-Aid for the real problem of a failed 12V battery, so if it has issues send it to the dealer so you can get a new battery and not worry about it.

Per Tim here, if the car is completely dead you should jump start it or put it on a really big charger to avoid boot looping the modules when the voltage is right at threshold. It's sort of a Catch 22 situation where you need enough charge so the modules can go to sleep before getting anywhere with the battery.

If when powering on, the big screen says "System off to save battery" is this a sign the 12v battery isn't functioning correctly, or is it just the car's way of saying "Ooh it's chilly this morning, better do all I can to save battery!!!" My car was built 26th February so shouldn't have the documented 12v battery issue.

 

[SnBGC]

The last couple of days I have been paying much closer attention to low voltage readings. So far I have observed around 14.4v for the first part of my drive. Then after 5 minutes or so, the voltage drops to 13.4 ish and a few minutes later around 12.9. Will then bounce back and forth between 12.9 and 13.4. Usually 12.9 while under power and 13.4 while stationary.

I have no idea if this is normal operation or not. Car had been running fine since around 9:00 am yesterday morning.

Is anyone else here able to see their voltage while driving and if so, are your readings about the same?

 

[themagicrobot]

In the second half of 2020 I was only using my Mustang V8 once a week. Even in summer every 3 or 4 weeks I would get "System off to save battery" on the screen. The 12v battery was definitely low every time......perhaps down to 50% and would need a big charge. It always worried me as you need power to drop the door glass to open the door to open the bonnet to charge the battery!!!
I still sometimes get "System off to save battery" on the MME but haven't yet resorted to charging the 12v battery. I guess when you charge the big battery the 12v gets a boost too. Not sure what would happen if you parked the car up for a month though.
Modern cars just have so much stuff running all the time in the background. Never had that problem with my 1967 Triumph Herald. When you switched it off it was off. (Good job as in those days it didn't even have a fuse box).

 

[Mach-Lee]

The last couple of days I have been paying much closer attention to low voltage readings. So far I have observed around 14.4v for the first part of my drive. Then after 5 minutes or so, the voltage drops to 13.4 ish and a few minutes later around 12.9. Will then bounce back and forth between 12.9 and 13.4. Usually 12.9 while under power and 13.4 while stationary.

I have no idea if this is normal operation or not. Car had been running fine since around 9:00 am yesterday morning.

Is anyone else here able to see their voltage while driving and if so, are your readings about the same?

That doesn’t seem right, it should stay at the 13.4V level while driving (after the initial 14.4V charge). 12.9V probably means the DC/DC is off and it’s draining the battery? That’s not good unless it’s brief. Low voltage can cause a module meltdown as you know. No reason to cycle the battery like that when it could remain constant.

Yes, other folks please go check yours if you are so equipped.

 

[KevinS]

Modern cars just have so much stuff running all the time in the background. Never had that problem with my 1967 Triumph Herald. When you switched it off it was off. (Good job as in those days it didn't even have a fuse box).

Assisted by Lucas, the Prince of Darkness...

 

[SnBGC]

That doesn’t seem right, it should stay at the 13.4V level while driving (after the initial 14.4V charge). 12.9V probably means the DC/DC is off and it’s draining the battery? That’s not good unless it’s brief. Low voltage can cause a module meltdown as you know. No reason to cycle the battery like that when it could remain constant.

Yes, other folks please go check yours if you are so equipped.

Yeah. Been monitoring.
I have noticed if the headlights are on then I see 14.4 volts constant.

Car still running great though. Will keep driving it until it doesn't go any more.

 

[kennethjk]

In my 911, I can plug the trickle charger into a cigarette lighter port to maintain the battery. am I correct that, that is not possible on the MME

 

[JimmyMachE]

The last couple of days I have been paying much closer attention to low voltage readings. So far I have observed around 14.4v for the first part of my drive. Then after 5 minutes or so, the voltage drops to 13.4 ish and a few minutes later around 12.9. Will then bounce back and forth between 12.9 and 13.4. Usually 12.9 while under power and 13.4 while stationary.

I have no idea if this is normal operation or not. Car had been running fine since around 9:00 am yesterday morning.

Is anyone else here able to see their voltage while driving and if so, are your readings about the same?

What was the aux battery SOC during these trips? Voltage is probably lower when the 12v battery is sufficiently charged. Headlights probably impose another control mode?

I started monitoring the aux battery SOC, control mode and voltage in Car Scanner Elm Obd2 app. I observed similar voltage variations but still too early to draw any conclusions...

 

[murphy62]

In my 911, I can plug the trickle charger into a cigarette lighter port to maintain the battery. am I correct that, that is not possible on the MME

That is correct. The power port is not directly connected to the battery. I haven't measured the time in the MME but my 2013 Fusion Energi turned the power ports off 70 minutes after the car was turned off.

 

[SnBGC]

What was the aux battery SOC during these trips? Voltage is probably lower when the 12v battery is sufficiently charged. Headlights probably impose another control mode?

I started monitoring the aux battery SOC, control mode and voltage in Car Scanner Elm Obd2 app. I observed similar voltage variations but still too early to draw any conclusions...

When you say Aux battery.....are you talking about the LVB?
I don't have any way to check SOC except for voltage readings.

I just have a bargain meter plugged into a power port. So far, the voltage readings are consistent with my earlier observations.

 

[murphy62]

13.42 volts is a charging voltage. A fully charged battery, after the surface charge has been eliminated, is 12.7 volts. A 50% charge is 12.2 volts. A 10% charge is 11.94 volts

 

[JimmyMachE]

When you say Aux battery.....are you talking about the LVB?
I don't have any way to check SOC except for voltage readings.

Yes, it turned out the obd2 adapter shows not only voltage of the auxiliary 12V LVB (low voltage battery), but some more LVB parameters.

Sponsored