Dead (really dead) 12V Battery

[Maverick Joe]

Update 2: After 24 hours of sitting the battery voltage has dropped from 12.57V to 12.39V.

This voltage drop seems excessive to me because if this drop is linear with time(-0.18V/day), the battery would probably be unable to crank the engine in less than a week. Think I should take it in? Any more diagnostics? Parasitic drain test using DMM?

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[Decayed]

Why not take it in and have it checked out?

BTW you can get a solar trickle charger on amazon. Just connect it to the 12v battery and put the panel in the side rear window that faces the sun.

 

[MakinDoForNow]

Update 2: After 24 hours of sitting the battery voltage has dropped from 12.57V to 12.39V.

This voltage drop seems excessive to me because if this drop is linear with time(-0.18V/day), the battery would probably be unable to crank the engine in less than a week. Think I should take it in? Any more diagnostics? Parasitic drain test using DMM?

Keep watching it. I do not know how it actually works but believe that soon after the 12v drops to some voltage (I guess 12.1 as that's the lowest I have seen on mine) the computer will cause the dc/dc converter to recharge the 12v to the saturation voltage switch over point to float charge and quit there to conserve the HVB. I expect this to be repeated as often as necessary until the SOC of the HVB drops to SOC that will trip the "your truck has entered sleep mode" status. Then you will put 12v on jump posts and the HVB will use it's 20-30% reserve capacity (or whatever it actually is) to start ice and charge everything. The 12v does not crank the ice the smaller of the two three phase high voltage motors spins the ice.

 

[Maverick Joe]

Keep watching it. I do not know how it actually works but believe that soon after the 12v drops to some voltage (I guess 12.1 as that's the lowest I have seen on mine) the computer will cause the dc/dc converter to recharge the 12v to the saturation voltage switch over point to float charge and quit there to conserve the HVB. I expect this to be repeated as often as necessary until the SOC of the HVB drops to SOC that will trip the "your truck has entered sleep mode" status. Then you will put 12v on jump posts and the HVB will use it's 20-30% reserve capacity (or whatever it actually is) to start ice and charge everything. The 12v does not crank the ice the smaller of the two three phase high voltage motors spins the ice.

That's interesting, thanks for your thoughts. If you are right though, then it makes the situation even more perplexing as to how the 12V battery got down to 2V in the 1st place. I believe the HVB is 1.1 kWh which should be plenty of energy for a long time. Way more than 3 weeks at least.

 

[Maverick Joe]

Why not take it in and have it checked out?

BTW you can get a solar trickle charger on amazon. Just connect it to the 12v battery and put the panel in the side rear window that faces the sun.

Thanks for the advice. Yeah, I am starting to lean towards taking it in.

 

[MakinDoForNow]

That's interesting, thanks for your thoughts. If you are right though, then it makes the situation even more perplexing as to how the 12V battery got down to 2V in the 1st place. I believe the HVB is 1.1 kWh which should be plenty of energy for a long time. Way more than 3 weeks at least.

The 12v battery furnishes current to continually watch things mine has to continually watch for key fob to approach. If Ford pass accesses truck it has to be ready to respond. God only knows what is continually and/or intermittently drawing 12v current. Some have reported that they turned off Ford pass as it was apparently draining 12v maybe accessing too frequently with some success. I do not remember where in manual the truck should be run for 15 minutes every two (maybe three) weeks. I do not know the parameters of the soc of the HVB but it will periodically be 100% charged but most of the time it will have some uncharged percentage to handle Regen braking , etc also the HVB will save enough reserve if you want to park and not start truck for two or three weeks. I personally would like to see auto start and run 15 minutes every ten days.

 

[Decayed]

Thanks for the advice. Yeah, I am starting to lean towards taking it in.

It might be something stupid simple. In any case that's what your warranty is for.

 

[Darnon]

That's interesting, thanks for your thoughts. If you are right though, then it makes the situation even more perplexing as to how the 12V battery got down to 2V in the 1st place. I believe the HVB is 1.1 kWh which should be plenty of energy for a long time. Way more than 3 weeks at least.

The 12V battery is only charged via the DC-DC converter when the truck is on. Otherwise the HVB battery circuit is physically disconnected.

 

[Maverick Joe]

Update 2: After 24 hours of sitting the battery voltage has dropped from 12.57V to 12.39V.

This voltage drop seems excessive to me because if this drop is linear with time(-0.18V/day), the battery would probably be unable to crank the engine in less than a week. Think I should take it in? Any more diagnostics? Parasitic drain test using DMM?

Update 3: after another 24 hours (48 continuous hours total) of non use the battery voltage has dropped to 12.33V.

 

[Glen Baker LLC]

I was wondering.
Does someone walk around dealers storage lots and start these rolling computers we now call cars and trucks? Do they disconnect the batteries?

 

[Deweyordeweynot]

My 2024 XLT Hybrid wouldn't start today...first time since driving it home from the dealer in January. Had to manually unlock the driver's side door, and flip the rear door open to access the 12v battery. The NOCO jump pack arrives tomorrow but I have a Battery Tender Plus connected directly to the battery terminals (the tender will not charge using the underhood power points). Hoping the tender gets enough volts into the battery so I can get to work tomorrow!

It gets driven nearly every day but only runs maybe 20 minutes each day, so the 12v may not be getting enough charge to replace what's used to maintain communication with FordPass and the keyfob and start the truck (I've always understood that the battery is not being used after the vehicle starts).

I've seen this is a common issue with the truck and that a 'fix' may be coming Q1 of 2025...

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