12V battery replacement poll

[B177y]

I chose "other" for the poll. I'll wait for gremlins or Ford app messages to start showing up then replace it.

I live it a mellow climate, not too hot and not too cold which batteries seem to "like". I also put over 30,000 miles/year so lots of DC/DC converter charging and lots of time on my EVSE charging, so the 12 volt is generally happy.

I purchased a load tester on the advice of a post by @RLXXI so I'll randomly run a load test or be able to do one at the first sign of a gremlin.

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[klossfam]

I chose "other" for the poll. I'll wait for gremlins or Ford app messages to start showing up then replace it.

I live it a mellow climate, not too hot and not too cold which batteries seem to "like". I also put over 30,000 miles/year so lots of DC/DC converter charging and lots of time on my EVSE charging, so the 12 volt is generally happy.

I purchased a load tester on the advice of a post by @RLXXI so I'll randomly run a load test or be able to do one at the first sign of a gremlin.

Well I can confirm in Western NY where we really don't get that cold (avg Jan high is 30 F) my 3 1/2 year old 75,500 mile original H3 is showing 100% SOH, 426 CCA (rated at 380).

My only concern is the number of charge cycles. If I don't drive the truck for a day and do a real short trip, the 12V will show a SOC of only 30-35% and my Viking Charger Tester will say the battery GOOD - Recharge.

Nothing too funky yet but I got the Discharge warning in the IP a couple times and the System Off to Save Power display pretty regularly on the center screen.

I do wish these H3s were more common like H4 and H5 AGMs. We've exclusively used H5 Weise AGMs on our family Hyundai and Kia EVs. $129 delivered. If that was the H3 deal, a new one would already be in the truck.

 

[21st Century Truck]

So as per my previous post here I took a good look this past Fall at my 12V battery, noticed it had bulging sides, ordered an OHMMU sodium 12V battery (only choice then available) and popped it in in late November or early December 2025.

I also mounted the optional OHMMU 12V battery monitor Bluetooth dongle at swap time, because why not?

We just got back from a three-week trip to Newfoundland Canada, 14 Dec thru 09 January total trip time. Two blizzards, an early polar cold freeze throughout the trip including on the way up and especially back down when we stayed with family in eastern Massachusetts... multiple times between the two blizzards and after them, it got seriously cold up there on the Rock (the local name for Newfoundland).

The OHMMU handled everything swimmingly throughout, so much so that I quit monitoring the 12V battery monitor halfway through the trip.

Very glad I had made the switch. My truck had about 81 K miles on it when I did, including some hot Arizona & Utah & Nevada driving this Summer which might have (??) contributed to the 12V OEM battery sides bulging.

 

[klossfam]

Might have been mentioned but a Motorcraft brand BAGM-H3 is $102 plus approx $12 fgt and $18 core at Rock Auto. Obviously put in your discount code for 5% off.

They have stock. Just ordered one and installed. Nov 2025 date code. Perfect. Just take the core back to O'Reillys for a $10 gift card. Easy.

Made it to 75.5k miles and did it due to the deep discharge it was doing. Showed 100% SOH but at 3.5 years old, that isn't good info from my Viking tester IMO.

 

[chl]

Just tested my Lightning (2023 Pro assembled 10-2023, delivered Jan 2024) 12v battery today using a UNI-T 673A battery tester and it read 100% SOH. It is 2 years old and always on a maintainer when not in use since about Sept 2024 when I started to hear about 12v battery problems and had an OTA fail for low 12v battery. It's been on a NOCO Genius1 since Nov 2025.

If you have to replace the battery, I believe it is an H3-size 12V AGM battery (35 Amp-hours, 380 CCA), Ford part number BAGM-H3.

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My 2012 Nissan Leaf 12v flooded battery is now over 13 years old, but still does the job.
It is a 45Ah 350 CCA flooded battery, Nissan part no: 24410-44S7A, with a "55B24L(S)" label on it.

The car was delivered Dec 2011, and the 12v has been on a maintainer since about Mar 2012.

The original maintainer died sometime in the Fall of 2025, and when I noticed that, I replaced it with a NOCO Genuis1, topped off the plates with distilled water (the level had gotten low) and charged/maintained it with the Noco for about a week.

I tested it today with the UNI-T and it read 80% SOH, rated "good."

 

[jwrezz]

I have been having to reset my "MyView" settings on the IPC regularly. This started happening after our January cold stretch where temps were regularly in the single digits for a couple weeks. Daytime highs may have hit 20F, but overnite was regularly 0-12 F. During this time and even earlier in Dec I had the battery saver warning come up 3 or 4 times. Since then I've either had to reprogram MyView regularly or keep it on the Noco charger every nite. I checked "other" because I'm going to either try one of the heated LiFePo4 battery options or an H4 50ah AGM with the battery tray mods posted in this forum.

 

[chl]

Is there a poll about how many of us have had 12v battery problems/replacements?

Seems like there were quite a few this last winter.

As for "SOH" there are several ways to measure it, some more accurate than others. SOH compares the present capacity to the original capacity and is expressed as a percentage.

Analyzing internal resistance and cold cranking amps with a battery tester is an easy method independent of the truck's method (whatever it is).

Since the truck does coulomb counting with the BMS, but often does not seem to fully charge the battery, and drift in the BMS is possible, I am not sure how much faith I would put in its report of SOC used to lookup SOH from a table as described below. There is some suggestion that perhaps the BMS coulomb counting number is corrected using terminal voltage.
[Edit for clarification in bold]

To get SOH using coulomb counting, the battery would be fully charged then discharged fully while measuring the current and then calculating the total energy (Ah) from that process.

With the battery disconnected from any loads, fully charging the battery and then measuring the terminal voltage after some period of 'rest' time (at least a hour) is a way to get the state of charge (SOC) and from that estimate the SOH. A fully charged healthy AGM battery should have a particular voltage corresponding to an SOC which can be read according to a table.

Sometimes an 80% SOC is used as the threshold for a healthy battery. For an AGM battery that corresponds to a reading of 12.5V fully charged at rest.

In the truck, the battery is really never truly at rest, there is always some small load, and it seems from reported data that the truck does not consistently fully charge the battery.

So terminal voltage while in the truck and not fully charged and measured before the battery has had a rest period is not a good way to accurately determine the SOC or the SOH.

What your car scanner is telling you is based on what the truck measures, and there are built-in inaccuracies in using terminal voltage and due to BMS drift.

For what it's worth.

 

[mr.Magoo]

Since the truck does coulomb counting with the BMS, but often does not seem to fully charge the battery, and drift in the BMS is possible, I am not sure how much faith I would put in its report of SOH.

It's probably wise to not put too much faith in the LVB SoH from the BMS since there isn't one being reported.

 

[chl]

It's probably wise to not put too much faith in the LVB SoH from the BMS since there isn't one being reported.

I should edit it to be clearer...it reports the LVB SOC, and from that owners calculate their SOH using a table for example as I mention in a later paragraph..

The problem is primarily with BMS is drift.

As time goes by small errors by the BMS sensor accumulate.

Also if the battery is overcharged and loses electrolyte or undercharged and has sulfates building up, that will/could skew the SOC measurements by the BMS

EDIT-INSERT: A battery with sulfate build-up on its plates can have a high terminal voltage after charging and resting but that drops under load rapidly. So terminal voltage alone is not adequate to know the real health of the battery.

Also in some cases to clear the errors the BMS has accumulated, the battery may need to be slow charged to 100% by an external maintainer. NOTE: it could also be reset afterwards using the reset procedure - like when putting in a new battery.

We know from owners data that the Lightning has all those faults.

We also know that owners report their carscanner data says their battery has a seemingly high SOC but exhibits weakness and even experience off-loading and shutdowns anyway.

I'll go back and see if I can make that point clearer.

Caveat: Not knowing all that much about the Lightning 12v BMS particulars, some of the above may not apply.

 

[Airforce]

I now have mine on a NOCO Genius1 trickle charger in AGM mode when not using the truck, or charging overnight which I expect to keep it healthy for a long time.

After reading about all the problems people have had on this and other forums, and having an OTA failure due to the 12v battery SOC being below 85% or so, I bought the NOCO Genius1 to avoid problems.

I put an SAE cord inside my charge port to make connecting the NOCO easier - just a small hole in the plastic and a 5 ft fused SAE cord with ring terminals to the battery (negative downstream of the BMS - connect at blue circles not red Xs) on the 6mm terminal screws:

BACKGROUND:

I've had lead-acid batteries, including AGM batteries, last over 14 years when on a trickle charger. As I learned in engineering school, unlike Li batteries, lead-acid batteries love being kept at 100% charge!

However, as I approach the end of my 3yr bumper-to-bumper warranty period I may unhook it from the truck and load-test it with my UT673A-675A battery tester.

If the indication is I need a replacement, I will use the 3yr warranty to get a new one.

If the test indication is the battery is still good, I will keep doing what I'm doing with trickle charging and feel confident it is not going to die any time soon.
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Disclaimer

I am an electrical engineer but not a licensed electrician.

The information provided in this post is provided for information purposes only and does not constitute any endorsement or recommendation. No warranty, expressed or implied, is made regarding the accuracy, adequacy, completeness, legality, reliability, or usefulness of any information found in this post. It is your responsibility to verify and investigate this information.

I recently replaced my LVB and added the Battery Tender. My HVB now charges up to 245 miles on 100% charge. 2024 SR XLT

 

[chl]

I recently replaced my LVB and added the Battery Tender. My HVB now charges up to 245 miles on 100% charge. 2024 SR XLT

That's good, but the two should not be related...unless the weak 12v battery was somehow affecting the range estimate? I have to think about that...

 

[chriserx]

That's good, but the two should not be related...unless the weak 12v battery was somehow affecting the range estimate? I have to think about that...

If it's attempting to charge a bad LVB while off plug it can waste energy as heat. I estimated at highway speed an extra 6% loss if this was the case (higher at lower speeds). If correct, I estimate that @Airforce original range to have been 230 if they'd kindly verify.

Edit: The estimate is actually 3-6% depending on the DCDC being 100A-200A. I haven't replaced my LVB, anyone know if doing so gives the GOM a clean slate? That's the other possibility.

 

[chl]

If it's attempting to charge a bad LVB while off plug it can waste energy as heat. I estimated at highway speed an extra 6% loss if this was the case (higher at lower speeds). If correct, I estimate that @Airforce original range to have been 230 if they'd kindly verify.

Edit: The estimate is actually 3-6% depending on the DCDC being 100A-200A. I haven't replaced my LVB, anyone know if doing so gives the GOM a clean slate? That's the other possibility.

From what others have measured, sometimes the LVB charging current does get up to 70A but only for a brief time, the charging current not the current being drawn from the battery to run the various truck components - I forget what those numbers were but they could be significant I suppose and they'd be higher if there was less energy stored in the 12v battery because it was weak.

And if the truck is using the AC or Heat fans, pumps, etc., and other 12v system loads, it could require more of the HVB energy to run things off the DC-DC converter when the battery is weak or low as well.

So I get your point.

But since it is only a 35Ah battery, I assumed the energy to charge it / keep it charged while driving compared to the HVB battery capacity would just be at the noise level.

The loads on the 12v system when running should hardly have any noticeable effect on range by comparison with the HVB running the drive motors, for example.

But who knows how the guess-o-meter reacts to a weak 12v battery?

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