Plug in to Maintain 12V Battery

[Secret Sauce]

It is a low 12v battery warning. But not the “super low” warning. As you stated it’s a separate alert.

Another way to read it? If you get that warning, your 12v is a little low. Just like it was for the post just prior to this one.

You can test it yourself next time you get the alert. My guess is you’ll be between 12.2 and 12.4 like others have posted here including myself.

Which isn't an actual problem, so why make it one? This is my point. The car is doing what it's designed to do. I'm seeing a lot of solutions in search of a problem.

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[Teslaeata]

How does one go about checking the voltage on the 12 battery? How can it be charged with a home charger if it dies?

You could either access your 12V battery which I understand is a bit of a faff because the trims under the bonnet need to come out which I have never felt the need to do, and drop a voltmeter across the terminals.

Alternatively, you could obtain an OBD link such as OBDlinkMX+ and download an app such as Car Scanner and that’ll read your 12V battery voltage along with loads of other stats and data which is of little more use than for just interest.

If you really feel the need, you could drop a battery charger between your 12V battery positive and the FRAME of the car if still connected to the car (not the negative terminal) make sure you use the correct charger for the battery.

However, you shouldn’t need to do any of this and concern yourself with your 12V battery, just keep the HV battery charged to a level that’s not too low, c50% if you intend leaving car for any length of time, and read the messages in the context they are intended, for information.

HV battery will maintain your 12V battery so don’t worry or overthink it. Be a “passenger” don’t try and over control things is my advise.

Just enjoy the car?

 

[Mach-Lee]

“System off to save battery” means the 12V battery is down to about 50% SoC. The radio is disabled to slow down the drain rate.

So it is a sign the battery is getting low. If you see that message often, it means your 12V battery is regularly being discharged down to 50% or less, which isn’t good for it (premature death).

If it keeps draining down to 40%, the car should automatically recharge it. But this is meant as a failsafe, not a regular thing. Those deep cycles prematurely kill the battery.

If you see “system off to save battery” you should immediately start the car and let the battery charge for a while with the car on.

Again, the way Ford designed the automatic recharge system is for occasional/failsafe usage and not daily/routine charging. Getting chronic “system off to save battery” messages are a symptom of a larger problem like some sort of drain or a battery that’s on the verge of failing.

The only time I ever see that message is if I deliberately leave the car on in accessory mode for too long. Otherwise I never see it. Don’t use accessory mode for more than a couple minutes, turn the car fully on.

 

[Teslaeata]

“System off to save battery” means the 12V battery is down to about 50% SoC. The radio is disabled to slow down the drain rate.

So it is a sign the battery is getting low. If you see that message often, it means your 12V battery is regularly being discharged down to 50% or less, which isn’t good for it (premature death).

If it keeps draining down to 40%, the car should automatically recharge it. But this is meant as a failsafe, not a regular thing. Again those deep cycles prematurely kill the battery.

If you see “system off to save battery” you should immediately start the car and let the battery charge for a while with the car on.

Again, the way Ford designed the automatic recharge system is for occasional/failsafe usage and not daily/routine charging. Getting chronic “system off to save battery” messages are a symptom of a larger problem like some sort of drain or a battery that’s on the verge of failing.

The only time I ever see that message is if I deliberately leave the car on in accessory mode for too long. Otherwise I never see it. Don’t use accessory mode for more than a couple minutes, turn the car fully on.

Can you reference the 50% and 40% you state as if it were fact within your knowledge?

Where does this information come from?

What measurements have you taken to demonstrate this?

 

[Mach1E]

Can you reference the 50% and 40% you state as if it were fact within your knowledge?

Where does this information come from?

What measurements have you taken to demonstrate this?

Volt ohm meter.

 

[Mach1E]

Which isn't an actual problem, so why make it one? This is my point. The car is doing what it's designed to do. I'm seeing a lot of solutions in search of a problem.

As always @Mach-Lee explains it better.

To be clear, I wasn’t insinuating it was a problem, just trying to help explain what it means to people who see the message.

For me, it was the first time I saw it, so I charged the battery.

If I keep seeing it, I’ll monitor it and possibly replace the battery. A dead 12v in our cars is a much bigger PITA than in an ICE. It’s not as simple as just getting a jump start and letting an alternator get you safely to your destination.

 

[mkhuffman]

Can you reference the 50% and 40% you state as if it were fact within your knowledge?

Where does this information come from?

What measurements have you taken to demonstrate this?

I measured it myself using CarScanner and it does just what Lee said: at 40% the HVB will charge the LVB. Of course 40% is very low and not good for the LVB, so whatever is causing it to get that low needs to be corrected.

See below for what happens when the LVB hits 40%.

 

[Mach-Lee]

Can you reference the 50% and 40% you state as if it were fact within your knowledge?

Where does this information come from?

What measurements have you taken to demonstrate this?

So when the "System off to save battery" message came up, I fired up my scan tool and saw the 12V SoC was at 50%. That was some months ago so I'll have to double check the exact %, but I'm pretty sure it's in that neighborhood.

Multiple threads in the past have observed the 40% recharge threshold, here's one. I've also observed it in my own 12V battery drain testing. EDIT: You can also see it in Mike's data graph above.

I've attached the technical description of the Mach-E charging system that describes the 12V recharge process in more detail.

I would also like to highlight this note from the bulletin:

 

[Mablanc]

These “Plug in to maintain the 12v” messages had essentially stopped a while ago after software updates and a visit to the dealer. Ever since the 6.1 software update they are back with a vengeance. Anyone else seeing this correlation?

I have had that 12V warning a hand full of time in three years, and mostly after washing the car, however, since the latest Powerup update, the 12V warning has popped twice in a week. Perhaps a ghost drain happening?

 

[mkhuffman]

So when the "System off to save battery" message came up, I fired up my scan tool and saw the 12V SoC was at 50%. That was some months ago so I'll have to double check the exact %, but I'm pretty sure it's in that neighborhood.

Multiple threads in the past have observed the 40% recharge threshold, here's one. I've also observed it in my own 12V battery drain testing. EDIT: You can also see it in Mike's data graph above.

I've attached the technical description of the Mach-E charging system that describes the 12V recharge process in more detail.

I would also like to highlight this note from the bulletin:

In the thread you referenced I posted that my LVB was not getting charged at 40% when unplugged. But that was before the dealer updated my car with FDRS. After then it worked properly.

So early MMEs definitely had a problem with maintaining the LVB when unplugged. None should have that problem now as long as the software is up to date.

 

[Mach-Lee]

In the thread you referenced I posted that my LVB was not getting charged at 40% when unplugged. But that was before the dealer updated my car with FDRS. After then it worked properly.

So early MMEs definitely had a problem with maintaining the LVB when unplugged. None should have that problem now as long as the software is up to date.

Yeah I have a suspicion they changed the minimum to 40% across-the-board rather than waiting 48 hours. So the behavior is probably a little different than when that document was originally written. There are still a bunch of Mach-E's with outdated BCM software out there that may not have those improvements yet.

 

[HuntingPudel]

Just a note on “System
Off th save battery:” It might trigger due to 12V SoC but it also has triggered for me based on time. I tend to like to have the radio on when I am working on the car. Knowing that the MME battery is stupidly small, I usually put it on a charger. I have had the car disable accessory mode many times while on the charger. ??

 

[RandyMache]

I follow this formula, ABPI=Always Be Plugged In.

That’s great, but I live in an apartment at the moment. Can’t be plugged in at all for L1/L2 charging. But I generally do drive daily. With regular use, will I have any 12 v issues?

 

[MachEMaster]

That’s great, but I live in an apartment at the moment. Can’t be plugged in at all for L1/L2 charging. But I generally do drive daily. With regular use, will I have any 12 v issues?

With daily use, your 12v battery should have no issues. The only thing that might affect it could be accessories such as improperly installed dashcams, or leaving things plugged in to the "cigarettte" lighter.

 

[RandyMache]

With daily use, your 12v battery should have no issues. The only thing that might affect it could be accessories such as improperly installed dashcams, or leaving things plugged in to the "cigarettte" lighter.

Very good, and understood. Thank you.

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