12V Battery Charging Facts

[guinn]

If that was normal, you‘d lose about 1/2% every 2 days from the HVB. Mine has set for two weeks without losing any.

ETA - those are ER numbers. You’d lose even more on your SR.

I think your math is off. If the 12V battery is charged 50% twice a day, that's one full charge per day. And you are saying that would be 1/4% of the HVB capacity (or 1/2% over 2 days). I think the HVB is much bigger than that! I have also left my car at the airport for about 5 days, and I saw no change in the HVB charge. So I agree with that.

Sponsored

 

[Maquis]

I think your math is off. If the 12V battery is charged 50% twice a day, that's one full charge per day. And you are saying that would be 1/4% of the HVB capacity (or 1/2% over 2 days). I think the HVB is much bigger than that! I have also left my car at the airport for about 5 days, and I saw no change in the HVB charge. So I agree with that.

Maybe….I ballparked it in my head. Let’s do it for real.

The 12V battery is 35AH. 35 x 12 = 420WH. If it discharged 45% in 10 hours, that’s roughly 0.45 kwh in a day or 0.9kWh in 2 days. 0.9 kWh / 91 kWh = 1%. So I was off, it‘s actually worse!

It‘s getting late - I’d be happy if someone else looked at - maybe I missed something.

 

[kennethjk]

Normal: LV car battery should not lose more than 10% charge per day. Not even close to that.

Source: It's possible to start a car after it has sat for a week. I've done it. Most people have. If it was losing 45% in 12 hours, the battery would be flat dead after two days of sitting.

I’ve left my car for 3 weeks without any issue. Starts right up.

 

[ThunderClap]

I've seen a tremendous amount of disinformation here about how the 12V battery charging system works. Here are the "facts" that I determined when my 12V battery ran down!

I hadn't driven my 2021 ME for 3 or 4 days. I had been getting warnings about the battery being low with a message to plug it into the charger. Since it was already plugged in, I ignored these messages. When I tried to use the car, it was dead. No response to anything. I started figuring out what to do and opened the frunk using the wires in the bumper. I then charged the 12V battery using a portable 12V charger until I could get things going (overnight).

I decided since I had access to the 12V battery, that I would monitor its state of charge for a while. I used a couple of small jumpers and a voltmeter. I also downloaded a chart showing voltage vs SOC for a sealed lead acid 12V battery. Then I noted the battery voltage over a couple of days.

The results were a little erratic, possibly due to a damaged battery (which the dealer later replaced) and the fact that the software bug had not been fixed, but generally the voltage dropped from 12.89 volts (~100% SOC) to about 12.36 volts (~55% SOC), and then it jumped back up to 100% SOC. The behavior was essentially the same, regardless of whether or not I had the L2 charger plugged in. And it usually took about 12 to 13 hours to drop from 100% to 55%.

This makes perfect sense. The HVB is not used to consistently keep the 12V battery at 100%. It drops down to about half-charge, and then the charging circuitry uses energy from the HVB to recharge the 12V battery. Since the HVB can keep the 12V battery charged for a very long time, there is no reason that leaving the car unused would ever run the 12V battery completely down. (Ford is saying to do something if you are going to leave the car for more than 30 days, but I suspect that is just being very cautious.) And remember, my results were the same with or without having the L2 charger plugged in. So, energy from the L2 charger is not being used directly to charge the 12V battery.

My problem turned out to be a software bug, and I had to jump through hoops to get the dealer to apply the fix, but that's another story!

I haven’t driven my car much in 2 days and had received 5 OtAs. And just 15 min ago got two notifications from fordpass.

What do I do? Should I plug it in? Or start the car and have it on for a while or what?

 

[Mach-Lee]

I haven’t driven my car much in 2 days and had received 5 OtAs. And just 15 min ago got two notifications from fordpass.

What do I do? Should I plug it in? Or start the car and have it on for a while or what?

What % is the high voltage at when you got that message?

I would turn it on for 30 minutes and read this: https://www.macheforum.com/site/thr...-system-drain-service-required-message.36140/

CSP 24P16 - Electrical System Drain Caused By HVAC Module, 12V Battery Test and Reset

 

[ThunderClap]

What % is the high voltage at when you got that message?

I would turn it on for 30 minutes and read this: https://www.macheforum.com/site/thr...-system-drain-service-required-message.36140/

Its at 47%

 

[medriver]

The car goes to sleep pretty aggressively and if functioning properly doesn't use very much 12v battery.

Just remember when sleeping if you open fordpass it's going to wake the car and use a few %, walking up to the sleeping car, a few %, PAAK wakeups, a few %.

The HVB->LVB charge is a salvage feature because the LVB is damaged by deep discharges.

The LVB charges VERY slowly when plugged in, this is noticeable when plugged in to a normal 15/20 AMP outlet, when you level 2 charge you don't notice as much because it still charges about the same rate but the HVB charges much faster comparatively.

 

[James III]

Hello Mach Lee, et al.
I just had my 21 AWD ER (build1) in for annual convenience check at the dealer here in the UK. They checked my battery too at the same time because I said it’s not holding a charge very well anymore. They put it on an analyser for a couple hours then decided to replace it just before warranty expired.
But after doing this, they began to monitor the SOC of the battery Turns out it was dropping to 45% overnight. They updated the BCM, and I stopped checking it on FordPass and Ford dashboard completely to leave it alone so they could monitor it properly. Now they found that on a regular Intermittently timed basis the BCM is clicking in and creating a draw on the battery which is more than normal even after the car goes to sleep.
They’ve had my MME for two weeks now and are trying to get help from Ford technical to find out what it is with BCM? They did update the BCM module and replaced the headlight switch because sometimes they say that can be a fault on this model. They’re doing this all under warranty and I’m not sure what’s going on? They wonder if it might be the fact that I had a friendly tech at a dealer use FORSCAN to enable the walkaway locking, which isn’t allowed in the UK due to Thatcham Insurance rules. So this dealer is now saying this is an unauthorised modification that could be the problem, and if Ford finds out they could void the warranty. ?
Thatcham is the same reason we have the ‘double locking’ option and don’t have PAAK. Our key is an old fiesta type that falls asleep after 30 seconds of no motion. So a key lying still doesn’t transmit and can’t be cloned. A key won’t start, unless the key is physically moving to activate the sensor. I could see that walking by the car with an active key would wake it, and cause a draw as pointed out in the FAQs. But how could Walk away locking cause a draw and mess up the BCM? They say my key is nowhere near the car, and locked in cupboard in the office.
Does anybody have any idea of what could be causing the BCM to behave as it is? I’d like to get my car back, And hand in this ICE Fiesta loaner! ?

Thanks guys

 

[MyMach-E is a Boat Anchor]

Read my post again. The LV battery should not lose anything per day. The battery management system charges it back to 100% after it drops to around 50%. Only when the HVB starts getting low does this become an issue.

My 21 CR1 12V is down to 25% after 2 days, then I get the dreaded yellow warning box. So yes I need a new BMS installed but Ford stopped covering them under warranty. My 12V battery only charges when the car is running. No charging at all when plugged into the 220V charger. Battery was new in February so it is unlikely a worn out battery. So now every 3 days I leave the trickle charger on overnight so I can drive the car.

 

[Mach-Lee]

Hello Mach Lee, et al.
I just had my 21 AWD ER (build1) in for annual convenience check at the dealer here in the UK. They checked my battery too at the same time because I said it’s not holding a charge very well anymore. They put it on an analyser for a couple hours then decided to replace it just before warranty expired.
But after doing this, they began to monitor the SOC of the battery Turns out it was dropping to 45% overnight. They updated the BCM, and I stopped checking it on FordPass and Ford dashboard completely to leave it alone so they could monitor it properly. Now they found that on a regular Intermittently timed basis the BCM is clicking in and creating a draw on the battery which is more than normal even after the car goes to sleep.
They’ve had my MME for two weeks now and are trying to get help from Ford technical to find out what it is with BCM? They did update the BCM module and replaced the headlight switch because sometimes they say that can be a fault on this model. They’re doing this all under warranty and I’m not sure what’s going on? They wonder if it might be the fact that I had a friendly tech at a dealer use FORSCAN to enable the walkaway locking, which isn’t allowed in the UK due to Thatcham Insurance rules. So this dealer is now saying this is an unauthorised modification that could be the problem, and if Ford finds out they could void the warranty. ?
Thatcham is the same reason we have the ‘double locking’ option and don’t have PAAK. Our key is an old fiesta type that falls asleep after 30 seconds of no motion. So a key lying still doesn’t transmit and can’t be cloned. A key won’t start, unless the key is physically moving to activate the sensor. I could see that walking by the car with an active key would wake it, and cause a draw as pointed out in the FAQs. But how could Walk away locking cause a draw and mess up the BCM? They say my key is nowhere near the car, and locked in cupboard in the office.
Does anybody have any idea of what could be causing the BCM to behave as it is? I’d like to get my car back, And hand in this ICE Fiesta loaner! ?

Thanks guys

How close are the keys being stored to the car? Keep them at least 10m away. Here are all the drain causes: https://www.macheforum.com/site/thr...-system-drain-service-required-message.36140/

I would put the BCM configuration back to factory and do additional testing. It is possible that could cause an issue since the feature isn't supported in the UK.

 

[William]

For the past three winters I have left my Mach-E in my Rochester, NY garage for 6 weeks at 50% SOC on the HVB. I use my ICE to visit CT during this time (I like to go South for the winter don't ya know). Every time I've returned, the car starts up just fine and I do not see any less SOC on the HVB than when I left. I don't know why, but this Mach-E has been wonderful!

 

[Just Lurking]

the car can automatically recharge the 12V battery when it gets critically low (<45%) while the car is off

Was the 24-PU0121-FTDI-FX update confirmed to change the 12V battery recharge logic? I was under the impression people thought it changed the 12V algorithm to be more battery-friendly (i.e. to start transferring power from HVB to LVB at a higher 12V SOC)?

 

[Mach-Lee]

Was the 24-PU0121-FTDI-FX update confirmed to change the 12V battery recharge logic? I was under the impression people thought it changed the 12V algorithm to be more battery-friendly (i.e. to start transferring power from HVB to LVB at a higher 12V SOC)?

Yes. Recharge threshold went from 35% to 45%.

 

[Just Lurking]

Yes. Recharge threshold went from 35% to 45%.

Wow. Better than before but beyond being surprised it was so low to start with, once they took the effort of updating the charging logic I'm surprised they didn't raise it higher, at least above 50%!

 

[Shayne]

My understanding was that the HCB never charges the LVB, unless the car is running, or the L2 charge is actually charging the car. Your post seems to indicate that the HVB DOES charge the LVB, even when not running or charging, it just doesn’t maintain it to 100%. So it sounds like the previous information I understood was not accurate, is that correct?

I was of the understanding that the HVB always charges the LVB and the contacts need to be closed for the 12V to charge.

Since the new app has no way of getting information from the car on demand this should eliminate the car being woke up and the 12V being used. All about not closing those contacts.

Wow. Better than before but beyond being surprised it was so low to start with, once they took the effort of updating the charging logic I'm surprised they didn't raise it higher, at least above 50%!

Agree 45% for a acid water battery state of charge is ridiculous for up here in the frozen tundra. Again all about not closing those robust contacts.

Sponsored