Is there a meter or method to determine the 12volt battery state of charge (SOC)?

[Mike G]

If you want a really accurate test of the battery without special equipment, you would need to disconnect it, fully charge it, note the terminal voltage with a voltmeter, let it sit for several hours (overnight), then use the voltmeter to measure the terminal voltage again - if it drops a lot from the fully charged measurement, then it has issues.

Of course you can get even more info using a battery tester, like CCA (Cold Cranking Amps), State of Heath, resistance, etc.

This is the one I use. And apparently it's -20% off for a limited time (as of the date I posted this).

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[Mike G]

And if you've never done a BMS learned values reset ever...might be a good idea to do it and then go for a drive of about an hour. As of today I've had my truck for 4+ years and am still on my original 12V battery. I do the reset about twice a year.

 

[carys98]

The steps for the procedure are listed above, and I have only one small correction to them....after you observe the little red battery icon on the IPC flash several times (step 6 above) and stop.....you need to shut the truck completely off, pause, and then turn it back on fully and go for a drive to charge up.

I seem to remember that opening and closing the door after powering off was recommended in one of the threads. I’ve been doing that ever since but wasn’t sure if it actually did anything.

 

[chl]

And if you've never done a BMS learned values reset ever...might be a good idea to do it and then go for a drive of about an hour. As of today I've had my truck for 4+ years and am still on my original 12V battery. I do the reset about twice a year.

Generally, a BMS is supposed to account for drift, by periodically checking terminal voltage and resetting for example, but I can't swear that the Ford Lightning 12v BMS does that or uses any other method. We know it uses coulomb counting (current in and out) to get the SOC number and I assume that is what the Car Scanner data is.

Having it on a maintainer has the same effect as manually forcing a resetting of the BMS.
The BMS keeps track of the terminal voltage and does coulomb counting.
When the BMS resets based on the terminal voltage, it allows the maintainer to fully charge the battery.
When the battery is actually fully charged, it will last many times the 3 year advertised lifetime.

Somewhere I heard that in the F-150, when the truck is "OFF" for 6 to 8 hours, so the 12v battery has settled, the terminal voltage is measured and the BMS is reset. I think I saw that in a You Tube video? If I find it again, I'll post it.

I think it also mentioned that if there are signs of drift problems, like shedding loads which causes strange behaviors and messages, then one should do the manual reset. Also need to do it when you change/replace the battery.

I think the video was about ICE F-150's which also had 12v battery problems.
But the Lightning has inhereted every other problem the ICE F-150's had - e.g., shifter malfunction and water leaks.

 

[chl]

This is the one I use. And apparently it's -20% off for a limited time (as of the date I posted this).

It's on sale because there is a newer version for full price ($150).

Some where I saw a review of a whole lot of battery testers when I bought mine (a few years ago).
For what I needed, the one I got did the job for a reasonable price (under $100).

It is not for heavy load testing using carbon-pile like pro-shop testers, but those generally cost more (over $100 and up).

 

[Maquis]

I seem to remember that opening and closing the door after powering off was recommended in one of the threads. I’ve been doing that ever since but wasn’t sure if it actually did anything.

Opening and closing the door is necessary to get out of the truck after doing the procedure!

 

[carys98]

Opening and closing the door is necessary to get out of the truck after doing the procedure!

Yeah, I went back and found what I was thinking about. It had to do with keeping the truck in neutral but it happened at the same time I was fighting BMS issues so I mixed the two together.

 

[GoodSam]

And if you've never done a BMS learned values reset ever...might be a good idea to do it and then go for a drive of about an hour. As of today I've had my truck for 4+ years and am still on my original 12V battery. I do the reset about twice a year.

Is it necessary to go on a drive or can one just leave the truck ON (in drive mode, not accessory) without driving?

 

[carys98]

Is it necessary to go on a drive or can one just leave the truck ON (in drive mode, not accessory) without driving?

You can just leave it on. Just have to turn off the shut down timer.

 

[chl]

I'm gonna go against the grain a bit here about using a maintainer. I have used one and have a pigtail connected up permanently to plug one in if I intend on leaving the truck while I'm away for more than two weeks (rare). I did this once while on a vacation two years ago.

But I don't find that it's necessary under normal circumstances. What I do find necessary (as has been mentioned above) is resetting the BMS logic roughly every three months. When I check my stats and notice my 12V SOC is below around 75% on successive days, and I've been actively driving the truck during that time, I will do the "BMS Learned Values Reset Dance" and then immediately go for a drive of at least an hour to fully charge my 12V battery back up.

I did this last week when I noticed my 12V SOC was at 78%, and now it's back up to 90%....and I still have my original 12V battery in my May of '22 built truck.

Can I get away with this forever? No. But it seems to have worked to extend the useful life of the original battery so far.

The steps for the procedure are listed above, and I have only one small correction to them....after you observe the little red battery icon on the IPC flash several times (step 6 above) and stop.....you need to shut the truck completely off, pause, and then turn it back on fully and go for a drive to charge up.

I believe THIS should be added to the BMS reset regime if you want an accurate SOC:

1) Fully charge your 12v battery before doing the reset procedure.

Rationale:

The BMS reset is used when you or the Ford techs put in a new, fully charged battery.

So, from what I understand, it causes the system to clear (get rid of) old collected data (from coulomb counting and any automatic resetting based on terminal voltage that may have occurred) about the battery and begin again. It will initially reset the SOC to 100% which will not be an accurate number unless the battery is fully charged (like a brand new battery should be).

So if your battery is NOT fully charged when the BMS reset is done, the system will not have an accurate SOC until it recalibrates itself based on the terminal voltage (or whatever other method / measurements it may use).

It should eventually recalibrate to the actual SOC over time - I believe the truck has to be OFF for something like 6 to 8 hours for this to happen from what I have read anyway.

SOH:

The SOH number is a percentage representing how much of the original capacity is still present in the battery.

As I understand it, the 12v BMS uses coulomb counting and terminal voltage measurements (and maybe other data like resistance) to come up with an SOH number, and it uses a particular 12v battery maximum 100% capacity (35AH) which is stored in the system.

So when the BMS reset is done, it will assume a 100% SOH.

But unless the battery is new and fully charged, and a 35AH battery, the initial SOH will not be correct.

Over time the BMS will recalibrate and calculate a more accurate SOH based on measurements taken when the truck if OFF for several hours, like with the SOC mentioned above, but it still uses a 35AH capacity number for 100% SOH.

So if you put in a larger capacity battery than 35AH (or smaller), I believe the capacity number should be changed using FDRS or FORscan to have accurate calculations.

If I got anything wrong in the above, please post the correct information.

I am basing the above in part on Ford publications about the 12v battery system, and information provided by other posts on this and other forums.

I should note that a Ford document, "414-01 Battery, Mounting and Cables 2022 F-150
General Procedures Procedure revision date: 03/8/2022, Battery Disconnect and Connect - Electric" mentions as the fisrt step to "De-energize the high voltage battery. Refer to: High Voltage System De-energizing - Electric (414-03A High Voltage Battery, Mounting and Cables, General Procedures)."

https://www.f150lightningforum.com/...ry-disconnect-and-connect-electric-pdf.70702/

I think this may be as a safety precaution when replacing the 12v battery because the HVB wiring might accidentally be touched when removing and replacing the 12v battery - but I do not know for sure.

Another precaution that was mentioned in the thread when disconnecting or replacing the 12v battery is do not disconnect the 12v battery during an OTA update - kind of obvious, but...

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