Bad 12V battery after 3 years

[Snakebitten]

Yeah, for whatever reason(s), Ford will disable the ICE completely, rather than USE the ICE to rescue itself by either charging the HV battery, or providing an ICE only limp mode for driving the truck to a dealership.

I can't imagine my Mach-E suddenly shutting itself down at 35% SOC.

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[HammaMan]

In winter the power bars start disappearing. Cold batt and below 30% power starts to disappear. I was around 15% last winter cold batt and it was ~60% retarded.

 

[Gros Ventre]

In an auctioneering arrangement the batteries are operating together. When a load is put on the circuit the battery with the higher voltage supplies it. When the two batteries are at equal states of charge they discharge equally and proportionally. The isolator separates the two so that the truck electronic systems don't see the voltage dip from starting the engine. That's an auctioneering arrangement designed to protect the electronic systems. IC engined vehicles didn't need this in days gone by because the electronics were far simpler and protection could be accomplished by disconnecting the small number of components. Now that the truck is "on all of the time," it is now simpler to disconnect the main battery, starter and a few other components and let them run independently during a start cycle. Call it what you want, the battery with the higher voltage (the Aux battery) runs the "rest of the truck" (and its computers) while the starting event is handled by the main battery at a bit lower voltage. That lower voltage is the characteristic dip due to the higher current through the main battery while spinning up the engine. If the two batteries were left connected together during the start cycle the smaller battery would attempt to also provide starting current. This would dip the voltage throughout the truck. When not in the start cycle the two batteries are connected. They then share load proportional to their state of charge and capacity rating. If one battery is faulty (as I suspect the OEM main batteries are) then the other will try and make up for it. This will drain the other battery also. This can then lead to system warnings. Since I didn't replace the aux battery when I replaced the main battery and all funny things stopped, I infer that the aux batteries do not have the same "illness" that the OEM main batteries have.

 

[Snakebitten]

So when they are connected, which you agree is almost all the time, and shortly after the underhood AGM has experienced a high amperage draw, along with the associated voltage drop, does the smaller auxiliary AGM with the higher SOC get taxed by the underhood AGM for any of its stored energy?

You know, propping it up a bit? ?

 

[HammaMan]

The aux batt is really just a transient buffer with a wee bit of reserve capacity (assuming stock) for everything in the truck sans its two starters (and one of the rad fans). Every start that opens the isolator, the load is handled by the DC/DC. The aux batt could be replaced with a modern capacitor and the truck would be none the wiser. A lot of modern vehicles will 'load shed' as soon as the key is in the 'start' position leaving the amperage to 'critical' loads for starting the vehicle (like HVAC, etc). Isolator protects the DC/DC from a high amp spike and allows for seamless starts.

The interesting part is that the small gauge wire used to connect up the isolator is already enough to protect the rest of the system from starting events if the isolator fails closed. Quite surprised they didn't just do that and let the aux batt blow a 50a fuse. The whole 125a / 4ga run back to the aux batt is because they already had it in the parts box for the PPOB ICE trucks. Surprised they didn't change it over to an 8ga 60a circuit. Oh well, it's a free 4ga power run if anyone needs it.

 

[GregScott]

Welp, it's only been 3 years and 37k miles, but ....i'm getting warnings about the vehicle turning off features to save battery life.
i know from past experience with gf's Ford Edge that it's a bad battery, but after only 3 years? that's a year or two early .
i'm not sure if it's going to last another month.
i have a month to decide if i'm buying out this lease or take the new 25' Lariat PB i have on order. i'd hate to drop $200 on a battery just to turn it in.

anyone else have a bad battery after 3 years?

Not too bad. Mine needed replacement at 11 months. Pathetic.

 

[FaaWrenchBndr]

I’ve heard auctioneering applied to diodes, but never batteries.


The aux battery's primary job is to power the vehicle's electronics & accessories when the main engine is off. Also during start-stop situations, and provides a backup power source to maintain critical functions. During high current draws like engine starting, its isolation from the main starter circuit; essentially acting as a buffer to prevent voltage drops when the engine cranks over. Thus BOOSTING the main battery since it’s wired parallel.

 

[Je1279]

Welp, it's only been 3 years and 37k miles, but ....i'm getting warnings about the vehicle turning off features to save battery life.
i know from past experience with gf's Ford Edge that it's a bad battery, but after only 3 years? that's a year or two early .
i'm not sure if it's going to last another month.
i have a month to decide if i'm buying out this lease or take the new 25' Lariat PB i have on order. i'd hate to drop $200 on a battery just to turn it in.

anyone else have a bad battery after 3 years?

Fear not. Just tell them that the battery tests fine if they question it...

 

[Baz]

I had my 12V AGM under hood battery replaced under warranty about 2 months ago and everything was great but since temps have dropped I noticed that welcome lighting & running board deploy was hit or miss even when standing right next to the truck with key fob. My truck is at the dealer for warranty work & new tires, so I had them check AUX and main batteries. The AUX battery hasn't been tested ever, only the main battery was checked in the past.

They did the Rotunda test on the AUX battery and it failed. The main battery tested good on the Rotunda test. They are going to replace the AUX battery.

I am curious if when my main battery was bad, was it causing damage to the AUX battery. Now that the AUX battery is bad, is it causing damage to the main battery?

 

[Sig Oris]

Osmosis.

Electron version?

I could be just plain wrong, as you put it so elegantly ?. But if that isolator isn't isolating the underhood AGM from the the truck's 12V buss, which it isn't except for very few seconds at a time, well.............. dem der batteries are one battery bank. No?

I admit that I'm not an expert at any of this stuff, but most of this is just logical.

So does anyone have a wiring diagram? That would help put this to rest.. sounds like the Aux Battery has a function like the watch battery in desktop computer. I’ve seen large a capacitor, many uFards, used in systems as a Keep Alive while power sources transition.

 

[Ries]

Welp, it's only been 3 years and 37k miles, but ....i'm getting warnings about the vehicle turning off features to save battery life.
i know from past experience with gf's Ford Edge that it's a bad battery, but after only 3 years? that's a year or two early .
i'm not sure if it's going to last another month.
i have a month to decide if i'm buying out this lease or take the new 25' Lariat PB i have on order. i'd hate to drop $200 on a battery just to turn it in.

anyone else have a bad battery after 3 years?

hey just picked up my truck from the dealer after a axle bolt shear recall fix. I had them look at this too as I was having the same issues. The issue is actually with the Ford Pass app. Make sure you’re running the latest version. This fixed my issue… thus far anyway.

 

[Gros Ventre]

The Aux Battery & the Main Battery are paralleled except when the start cycle is engaged. When the starter button is pressed a relay opens up separating the Main Battery, starter motor and a few others from the rest of the truck's electrical system. This prevents the electronics from seeing the voltage dip inherent in the starter motor's large current draw on the Main Battery. The Aux battery does not, alone, power the truck's electronics when the truck is off. Could either battery drag down the other, well maybe. To say that the Aux Battery is boosting the Main Battery when not in start cycle or off, is a misnomer. Its there only to support the truck electronics when starting. That it's in parallel with the Main Battery and thus contributes to current flow is true, but there is no need for that. The Main Battery is large enough to support things on its own.

 

[Snakebitten]

As far as I can tell the auxiliary battery is only auxiliary for the briefest of moment.

Only when it is isolated

Otherwise it's just a parallel member of a 12V bank of batteries sharing load with the other members

 

[Je1279]

To simplify the equation a bit, my '23 XLT does not have an aux battery and the primary battery got to a point at ~20 months after a custom order purchase where it required manual charging every 2-3 days. I chose to purchase an Everstart Platinum AGM H7 to replace it and have had no issues since, even with overnight temps down into the mid teens. I am by no means advising to ignore the status of the aux battery, just know that the primary battery is suspect even without it.

 

[EcoBeastCA]

What are y'all doing to get Ford to replace a bad battery? I know mine is bad because it will float around 11.9V ignition off, which is obviously way too low. My service advisor tells me though that Ford (Canada?) is really sticky on replacing batteries and unless the battery test performed by the dealership tests "BAD" they just keep charging up the damn thing.

Another point towards bad battery - my auto stop/start hadn't kicked in for at least a month. But when I took a small road trip and had the truck on for a few hours, all of the sudden auto stop/start begins working again, even in very cold temperatures. I know that it pretty much only goes off of battery SOC to enable/disable, so this should be further evidence.

Truck is a year old. I shouldn't have to be paying hundreds of dollars out of pocket for a new battery because Ford is being cheap. Any ideas?

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