Ford BMS oddities with AGM battery

[Klutch9]

Today I replaced an old flooded battery with an agm in my 2016 Explorer. Same group size and very similar CCA as the flooded battery. I do have access to Forscan, but I’ve read on many Ford vehicles you can reset the BMS (battery monitoring system) without it, and that applies to my vehicle as well. Just out of curiosity, I measured the voltage at idle with the old flooded battery, and it was always 14.0-14.8 volts roughly. Same while driving (I have a scangauge). I did a BMS reset with the old battery just for fun, and the voltages were the same.

Now after installing an AGM, and doing another BMS reset, the vehicle usually sits at 12.66 volts at idle. While driving, it’s 12.9-13.0 volts usually, but will occasionally jump to 14.8ish and slowly taper back down to 13.0. Then in park, back to 12.66 volts.

I’ve read elsewhere that the BMS will adjust the first couple of days after installing a new battery. I’ve also read that the BMS selected an AGM profile on its own, as confirmed by a member using Forscan. I suppose I’ll watch the voltage over the next couple days and see what happens. The battery was only a couple months old and 12.55v out of the box, so decently charged.

 

[Jetronic]

Mine has an AGM and constantly keeps the voltage at 13.8/13.9V. I'm happy with that, it should keep the battery fairly full and definitely not depleting further.

If I start the car with lights and HVAC off, it will do roughly what yours does: battery voltage at idle and while driving, then up to 14.4V ish when braking or coasting. That's the mileage testing mode I guess.

 

[Klutch9]

Mine has an AGM and constantly keeps the voltage at 13.8/13.9V. I'm happy with that, it should keep the battery fairly full and definitely not depleting further.

If I start the car with lights and HVAC off, it will do roughly what yours does: battery voltage at idle and while driving, then up to 14.4V ish when braking or coasting. That's the mileage testing mode I guess.

I noticed a couple times on my short drive that the voltage rose while braking/coasting as well. And if I drove long enough in between with no braking, the voltage would rise on its own briefly then drop back down.

 

[Hall]

I’ve also read that the BMS selected an AGM profile on its own, as confirmed by a member using Forscan.

I don't believe that the BMS is "smart" in the sense that it can detect and change the battery type. You probably want to find the proper code for an AGM battery in the same or similar size (or match the CCA as close as possible) and code it in with FORScan. There are tons of lists and spreadsheets out there with this data and you don't need to use an Explorer-specific one, as I understand it. You can use the code from a Fusion, F-150, etc and from what I saw in the past (no longer have a Ford), the F-150 forums have the most data to reference.

 

[Klutch9]

I don't believe that the BMS is "smart" in the sense that it can detect and change the battery type. You probably want to find the proper code for an AGM battery in the same or similar size (or match the CCA as close as possible) and code it in with FORScan. There are tons of lists and spreadsheets out there with this data and you don't need to use an Explorer-specific one, as I understand it. You can use the code from a Fusion, F-150, etc and from what I saw in the past (no longer have a Ford), the F-150 forums have the most data to reference.

If I do this, do I try to match the CCA or the amp-hour size? I’ve already looked through the options in Forscan, and there isn’t one that matches both. Plus, this battery routinely tests way above the rated CCA from reviews I’ve seen.

 

[Hall]

or the amp-hour size

Use Ah. I couldn't remember the specifics anymore though I knew CCA was one. Can you measure Ah and use the actual value of your battery ? I don't know if you can.... If I measured 825 CCA while the rating was 750, yeah, I'd use 800-825.

 

[Klutch9]

Use Ah. I couldn't remember the specifics anymore though I knew CCA was one. Can you measure Ah and use the actual value of your battery ? I don't know if you can.... If I measured 825 CCA while the rating was 750, yeah, I'd use 800-825.

CCA is 750 but some test it at over 900 out of the box. AH is 68 though, so I’d probably use the 70 AH setting in Forscan.

 

[Hall]

Yours might be 750 so unless you test it, you can't use other numbers. CCA is only for starting anyway, not what BMS cares about. BMS, as I understand it, makes the alternator a "smart" alternator. It engages/disengages as needed for fuel economy (I think). This is where Ah matters more.

 

[Klutch9]

After letting it sit a couple hours, I started the car again and let it run for a few minutes. Put it in gear, back into park. It was at 13.6v the whole time. I’ll see how it is tomorrow. I’ll have numerous trips then and will see how it acts.

 

[meep]

I’ve got a pretty detailed post around here for the volt swings in my ‘18. Ford targets 80% SOC in mine. 12.4 on a temperate day at cruise, 14.4 or so during deceleration, always shifting back and forth. 13.5 solid if lights are on or high AC. From what I recall reading, it’s worth more mpg that auto-start/stop.

 

[Klutch9]

I’ve got a pretty detailed post around here for the volt swings in my ‘18. Ford targets 80% SOC in mine. 12.4 on a temperate day at cruise, 14.4 or so during deceleration, always shifting back and forth. 13.5 solid if lights are on or high AC. From what I recall reading, it’s worth more mpg that auto-start/stop.

Ah yep, you’re the one I was thinking of! It is interesting how the system works. For now I’ll leave the target SOC at 80%, and I won’t mess with the battery type yet. The AGM installed is the same size and CCA as the flooded battery it replaced, and there’s no exact match for it in the Forscan settings.

 

[zzyzzx]

Is disabling BMS with Forscan an option?

 

[Klutch9]

Is disabling BMS with Forscan an option?

I’m pretty sure it is.

 

[meep]

Yes, bms can be turned off. Keeps it around 13.8 if memory serves. It might be my imagination but the transmission seemed ever so slightly more consistent with its shifts at first. I later turned it back on with a higher SOC (88?) and didn’t notice degradation. At above 92% SOC it spends a lot more time at a higher voltage.

Why did I turn it back on? Man, call it a sensitive butt dyno, but the truck felt somehow more “effortless” with bms enabled, and I liked how that felt.

 

[Klutch9]

I decided to change the battery profile to AGM last night (chose 70AH, mine is a 68AH so pretty close), and did another BMS reset. I only drove it once, but the charging voltage was very low to start again... 12.6 at idle, around 13.0 while driving. I'm guessing that when I drive today it will be higher, like it was before.

 

[meep]

It won’t stay 13.0 long. 12.4-12.6 cruise. 14.5 ish on decelerate. 12.4 at idle. 14.8 at first start for 30 seconds.


13.5 lights on or AC over 2/3.

Once per month, 14+ volts for a few hours.

I have a gauge permanently mounted in my headliner.

 

[Torrid]

Is disabling BMS with Forscan an option?

If you unplug the sensor ring that goes around the lead at the battery the BMS shuts down and you'll see the voltage immediately go up. I did this with our '14 Edge because as much as it short tripped at the time, it wouldn't charge enough to start reliably in the winter even with a new battery. Unplugging the sensor alleviated the issue. It did not give us any warning lights.

 

[Klutch9]

It won’t stay 13.0 long. 12.4-12.6 cruise. 14.5 ish on decelerate. 12.4 at idle. 14.8 at first start for 30 seconds.


13.5 lights on or AC over 2/3.

Once per month, 14+ volts for a few hours.

I have a gauge permanently mounted in my headliner.

Oddly, after that first day, the voltage sits between 14.3 and 14.9 volts all the time. Never really drops down.

 

[MParr]

Turn the ignition to the on position.
Flash the high beams 5 times.
Hit the brake pedal 3 times.
Wait for the battery indicator to go off.
Done.
It will take a tank or two of gas before the average fuel mileage to recalculate.

 

[KJSmith]

Turn the ignition to the on position.
Flash the high beams 5 times.
Hit the brake pedal 3 times.
Wait for the battery indicator to go off.

I end up flashing 5 times, hitting the brake 5 times....
Then wait for the battery light to blink 3 times.

If you want to be extra cautious, do that and then let your vehicle sit untouched for 8 hrs,