2024 having 12v low voltage battery issues with my Hybrid...

[HeyBales]

Won’t the BMS reset by itself after a few days of driving?

No indication it does that.
That's why it's a scan tool function or manual operation the manual says to do.

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[CurtisB]

I put in my own AGM Battery and reset the BMS in May. Only 3 "sleep issues" since then but no completely dead battery. Prior to putting in an AGM battery, I put in a new Die Hard Flooded battery..............it lasted 8 weeks and then completley died. In my non scientific opinion, the AGM battery works. It charges faster and keeps the charge longer.

I might note that the original flooded battery that came with the truck didn't last 6 weeks!! And after reading about suggestions here in this forum, I bought a new Die Hard, but I didn't find out about AGM batteries until after I bought the Die Hard.

Now there are those who will argue about my decision, but that's what forums are for. With the Flooded batteries, after receiving the "sleep" and no dome light situations, I had to charge the battery back up overnight. With the AGM battery, after the 3 different sleep notifications over the last 4 months, I simply drive the truck and it charges back up.

Also, I was gone for 5 days with my truck in the driveway under 106 degree heat. Did not get a "sleep" message while I was gone and it started right up upon my return. The AGM battery made a difference for me.

 

[HSBII]

I put in my own AGM Battery and reset the BMS in May. Only 3 "sleep issues" since then but no completely dead battery. Prior to putting in an AGM battery, I put in a new Die Hard Flooded battery..............it lasted 8 weeks and then completley died. In my non scientific opinion, the AGM battery works. It charges faster and keeps the charge longer.

I might note that the original flooded battery that came with the truck didn't last 6 weeks!! And after reading about suggestions here in this forum, I bought a new Die Hard, but I didn't find out about AGM batteries until after I bought the Die Hard.

Now there are those who will argue about my decision, but that's what forums are for. With the Flooded batteries, after receiving the "sleep" and no dome light situations, I had to charge the battery back up overnight. With the AGM battery, after the 3 different sleep notifications over the last 4 months, I simply drive the truck and it charges back up.

Also, I was gone for 5 days with my truck in the driveway under 106 degree heat. Did not get a "sleep" message while I was gone and it started right up upon my return. The AGM battery made a difference for me.

Interesting I have read several posts of guys who have switched to AGM and still had issues but not as frequent.. I bought my truck at the first of May and have only had 2 low voltage issues (IE no dome lights) one in late June and again earlier this month…
There was no issues with the truck turning on and driving I put the charger on it both times to charge up the battery… Think im leaning towards installing a onboard battery charger and just charge the battery once a week….

 

[Derwood]

Interesting I have read several posts of guys who have switched to AGM and still had issues but not as frequent.. I bought my truck at the first of May and have only had 2 low voltage issues (IE no dome lights) one in late June and again earlier this month…
There was no issues with the truck turning on and driving I put the charger on it both times to charge up the battery… Think im leaning towards installing a onboard battery charger and just charge the battery once a week….

I've already had my cheap factory battery replaced twice in one year. Am in sleep mode almost all the time but since I live five min from the dealership and only drive small local miles I don't give a shit. Truck has never died completely and I have remote start for the winter months. A small nusiance is all it's been for me. Ford obviously doesn't want to deal with the issue sadly enough though

 

[HeyBales]

I think I can discern from this what method our BMS must be using.
Just not completely the correct method.
I'm thinking it's not the trademarked method that likely has a higher cost to it.

https://batteryuniversity.com/article/bu-903-how-to-measure-state-of-charge

 

[Maxximus]

As best I can explain the BMS issue is this. First off the BMS if it is the same as the ecoboost engines should be the black box on the negative cable right before the battery terminal connector. It will also have sensor connector and wire which among other things allows it to talk to the BCM module. With the information it monitors i.e. current, voltage and voltage temp it passes that along to the BCM which uses that to determine the battery's charge state whether it is 100%, 90% etc. Now if the current from a charge goes around it on the terminal the BCM can't update that correctly. If that state got too low and it started soft offing circuits like the dome lights even if you do charge the battery it will still keep doing it. The BCM has no way of knowing otherwise. If it keeps doing that eventually even though the battery maybe charged it will think it is at a low enough level that hard off's start like permanent shut off of the auto start/stop system which can only be reneabled by reseting the BMS.

That is why the negative has to be connected somewhere before the BMS sensor not behind it when charging. The surefire way to fix that is to get the BCM to relearn the battery's charge status and in turn recalculate the battery's life. The only 2 ways I know that it does is when you change the battery or you reset the BMS.

So can anyone include pictures for how to attach a trickle charger correctly? Where do you find a chassis ground inside the back seat under the seat where the battery is located?

 

[Darnon]

So can anyone include pictures for how to attach a trickle charger correctly? Where do you find a chassis ground inside the back seat under the seat where the battery is located?

The ground connector bolts to the floorpan right adjacent to the battery.

 

[Maxximus]

The ground connector bolts to the floorpan right adjacent to the battery.

Thank you! So where is the positive suppose to go if not to the actual positive post so this BMS BCM sees the charge correctly? Very confusing sorry.

 

[Darnon]

Thank you! So where is the positive suppose to go if not to the actual positive post so this BMS BCM sees the charge correctly? Very confusing sorry.

The positive can go on the battery. The current sensor is on the ground terminal of the battery; it's pretty obvious. Basically just don't connect to the battery ground post directly or slip a terminal beneath the terminal's pinch screw.

 

[huunvubu]

The problem with that is: that socket does not power up until you turn on the ignition or at least the accessory power. Then the 12v battery is getting power from the inverter. You need to be able to get a reading before even opening a door to get a good indication, if possible.

This is partially incorrect information.

It is TRUE that you have to turn the key to get power to the accessory port.

However you are wrong that in "accessory power" the DC-to-DC converter supplies power.

With the key turned partially to "accessory power" and not all the way to "Ready" the accessory port will show actual battery voltage.

Accessory Mode showing 12.1 volts from the battery.

It is a good idea to check battery voltage in the accessory mode as it puts a small load on the battery.

When the key is turned fully to the "Ready" state the DC-to-DC converter supplies power.

Ready Mode showing 14.6 volts from the DC-to-DC converter.

 

[Darnon]

At least on mine there is some slight voltage rise in accessory versus the battery actual voltage. Possibly bleedover from the precharge capacitor?

(And, pedantically, it's a converter not an inverter since it's just stepping DC to DC)

 

[huunvubu]

At least on mine there is some slight voltage rise in accessory versus the battery actual voltage. Possibly bleedover from the pre-charge capacitor?

(And, pedantically, it's a converter not an inverter since it's just stepping DC to DC)

The pre-charge capacitor I know of is for the HV battery so that the contactors do not spark when closed.

I have not heard of a pre-charge capacitor for the 12 Volt Battery.

 

[Maxximus]

The positive can go on the battery. The current sensor is on the ground terminal of the battery; it's pretty obvious. Basically just don't connect to the battery ground post directly or slip a terminal beneath the terminal's pinch screw.

Thanks so much for your help! I have not had any problems at all as of now but approaching winter here in Ohio and I work from home 3 days a week and don't drive much so I thought about leaving a pigtail on the battery and plug in the trickle charger if it's going to sit 3-5 days a week.

 

[Darnon]

The pre-charge capacitor I know of is for the HV battery so that the contactors do not spark when closed.

I have not heard of a pre-charge capacitor for the 12 Volt Battery.

Correct, it's for the HV side. But the DC-DC seems to outputting something even though in theory the main HV contactor shouldn't be closed yet. Just double-checked and it'll go from 12.3v resting off to >14v in accessory. Measured at the under hood terminals.

 

[bishop0114]

I had that issue, they had to replace the battery twice and now it is fine.

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