Plug in to Maintain 12V Battery

[Teslaeata]

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:

Really interesting, thanks.

Whilst the document is relevant to police and other responders rather than retail users such as us lot, it is interesting that our AGM battery is so tiny though the limit for accessory use is well in excess of that which I expect any of us could use with our toy dash cams etc.

For context, I don’t think those percentages of 12V battery charge levels are anthing to get excited about because 40% charge doesn’t mean 40% of 12V or even the full voltage of an AGM battery which would be 14.2V or more.

The attached chart illustrates.

So, if we are using our cars properly, we park them properly, do not continually drain our LV batteries exceeding the accessory limit of 65A and we maintain our HV battery level we should have no problem with our 12V batteries.

I don’t think we should read anything into information notices, overthink things, misinterpret data obtained by OBD devices and we should not try to control things which are already under control by the car’s systems.

Plugged in or not, our 12V batteries will be charged and conditioned when required and their failures are rare.

I wouldn’t let it all spoil my life or worry me.

Just enjoy your ‘Stangs, people?

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[RandyMache]

Remember, our 12v batteries don’t have to crank over an engine. So no need to be a huge battery.

 

[Maquis]

Remember, our 12v batteries don’t have to crank over an engine. So no need to be a huge battery.

There are two facets to battery size. Cold cranking amps (CCA) which is a measure of its ability to deliver large levels of power for a short time (engine cranking) and amp-hours (A-H) which is a measure of how much energy it can store. We don’t need the high CCA, but a few more A-H might be useful, especially if powering accessories when the car isn’t running.

 

[RandyMache]

There are two facets to battery size. Cold cranking amps (CCA) which is a measure of its ability to deliver large levels of power for a short time (engine cranking) and amp-hours (A-H) which is a measure of how much energy it can store. We don’t need the high CCA, but a few more A-H might be useful, especially if powering accessories when the car isn’t running.

Everything could always be better, right….. I don’t disagree with you.

 

[Mach1E]

Well, here’s my 12v update.

I charged it a week ago via a plug in charger.

Drove my car every day this week.

Charged the car to 90% twice.

And my LVB is back down to 12.3……… so annoying.

I wish I could blame a software update but I haven’t gotten any of the recent ones (my last was the first week of August).

What gives?

 

[Teslaeata]

Well, here’s my 12v update.

I charged it a week ago via a plug in charger.

Drove my car every day this week.

Charged the car to 90% twice.

And my LVB is back down to 12.3……… so annoying.

I wish I could blame a software update but I haven’t gotten any of the recent ones (my last was the first week of August).

What gives?

What is there to worry about??‍

12.3V is what? 60%?

The system hasn’t allowed the LVB to let you down. Why the worry??‍

 

[Mach1E]

What is there to worry about??‍

12.3V is what? 60%?

The system hasn’t allowed the LVB to let you down. Why the worry??‍

Because it’s low and I was getting the alerts that told me it’s low. It’s also a new problem.

I shouldn’t be low unless something is wrong. And like was mentioned earlier, a low 12v is a much larger problem in these cars. Can leave you stranded on the road and need a tow.

 

[Teslaeata]

Because it’s low and I was getting the alerts that told me it’s low. It’s also a new problem.

I shouldn’t be low unless something is wrong. And like was mentioned earlier, a low 12v is a much larger problem in these cars. Can leave you stranded on the road and need a tow.

So,

What is there to worry about??‍

12.3V is what? 60%?

The system hasn’t allowed the LVB to let you down. Why the worry??‍

The car don’t see 12.3V (60%) as a problem because……….

 

[Teslaeata]

Worry thee not, my child ?

 

[Fixbear]

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?

Exact same thing I have. Only thing changed was 6.1.0. Same routine as before but less longer trips. And the average temperature has dropped about 15 degrees.

 

[Mach1E]

So,

What is there to worry about??‍

12.3V is what? 60%?

The system hasn’t allowed the LVB to let you down. Why the worry??‍

The car don’t see 12.3V (60%) as a problem because……….

Because it hasn’t done this before (drain while driving daily and charging every few days) and like people have posted, it’s not good for the LVB to keep getting low. I’m also wondering if the lower battery charge is related to me not getting any OTA updates the last 3 months.

If your tires have a slow leak, you don’t wait til they’re completely flat to do something.

 

[Teslaeata]

Because it hasn’t done this before (drain while driving daily and charging every few days) and like people have posted, it’s not good for the LVB to keep getting low. I’m also wondering if the lower battery charge is related to me not getting any OTA updates the last 3 months.

If your tires have a slow leak, you don’t wait til they’re completely flat to do something.

Am concerned that you’re worrying yourself unduly as many on the forum seem to do.

That it’s not done this before is not necessarily something to worry about because it may mean very little and you might be looking at a condition which is not problematic.

Be wary of other stuff posted, remember this a forum!

Also, your “low” may not actually be low if it’s not below 40%, or 30%, when the car’s systems take over and HV/LV charge.

Failure to receive OTA updates won’t discharge a 12v battery.

The tyre scenario is entirely irrelevant to your managed 12V battery system because there is no system which checks and re-pressurises your tyres when/if their inflation pressures fluctuate.

At the risk of overthinking and undue worry, because the pre-requisite conditions are so numerous and their analysis are outside the expertise of the layman to even understand and check a dealer probably ought to take a look.

Prerequisite conditions are summarised in image attached, fuller details to be found in the linked document already posted here but I would read it VERY carefully and understand the context of each and every part trying not to read what you want into any part.

https://www.macheforum.com/site/attachments/220738055952p-033r2_policemodbulletin_rev0-pdf.109570/

 

[mkhuffman]

Because it hasn’t done this before (drain while driving daily and charging every few days) and like people have posted, it’s not good for the LVB to keep getting low. I’m also wondering if the lower battery charge is related to me not getting any OTA updates the last 3 months.

If your tires have a slow leak, you don’t wait til they’re completely flat to do something.

If I were you, I would recondition the battery and see if that helps.

 

[dj_stang]

It should automatically recharge itself when it gets down to 40-50% as long as the high voltage battery isn't low (>15%). However for whatever reason(s) that doesn't always work. There was some bad software in the initial Mach-E's, things are better now.

Yes and yes. Apparently a lot of retired and WFH people own this car, and don't even drive 20 miles per week, so in those use cases the 12V will become low from lack of driving and charging hours.

It is best to keep the 12V around 90% charged, charging to 100% all the time can put extra stress on the plates and cause accelerated grid corrosion. Cycling lead acid batteries also contributes to their demise. With normal use the 12V will typically be around 70-90% SoC. Things could be programmed a little bit better to start the recharge process sooner before a load shed occurs ("System off to save battery"), that way the customer doesn't notice.

@Mach-Lee could you help me reconcile these two statements? It seems in the first message that the car will maintain the LVB as long as the HVB isn’t low. But in the second message that it will only maintain while charging.

 

[Teslaeata]

@Mach-Lee could you help me reconcile these two statements? It seems in the first message that the car will maintain the LVB as long as the HVB isn’t low. But in the second message that it will only maintain while charging.

Ford say this:


“While ignition is off, if 12V battery reaches 40% state of charge, then vehicle waits 48 hours , before the DC-DC transfers 300 Watt-hours of energy to recharge the 12V battery. The HV power comes from EITHER HV battery OR wall power while on plug. If the 12V battery state of charge reaches 30%, then this HV to LV energy transfer happens immediately with no
delay.”

To assist with an understanding of LV percentages, see attached chart, 40% or even 30% SoC for LV isn’t as low as it seems.

There are other factors which prevent LV charging from HV but so long as we park our cars properly in Park etc shouldn’t affect us.

There is battery management which means we need not concern ourselves about plugging in unless HV is under 15% SoC which is a percentage directly quoted from Ford.

The message we see from time to time which is purely for information informing that system is shutting down to conserve energy does NOT mean jump up, spin around and start panicking because your LV battery’s dying the death and, as far as I can tell, the other message instructing plugging in for a HV charge is often erroneous unless HV is under 15% SoC because some reported software updates removed such messages unless, of course, HV SoC is under 15%.

I’ve seen reports of people charging, reconditioning, desulphating their AGM LV battery which should be avoided unless you really are a battery expert.

My advice is don’t worry, you shouldn’t need to, let the ‘Stang manage your LV battery.

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