Battery SOC

[Brian_B]

Try a BMS reset. The data in the BMS gets corrupted after some time. I see if all the time when I check VINs for OTA failures.

Yup that will be my next step before jumping to new battery.

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[Greg2060]

I do agree that it's very possible my battery is on the fritz - I never seem to see the trickle charger put many amps back into the battery before it says it's at full charge. My Bronco seems to spend an awful lot of time lately at 14.6-15.2V, so I ~think~ the BMS sees a low state of charge and is trying to recharge. For instance, I just did a 500 mile trip, and it wasn't until about halfway on the leg back that I finally saw the voltage drop to the "normal" 13V range. And here I am, just a week later, and now I'm seeing the Power Point drop out and back at 15.2V pretty much non-stop.

Do you know how or if the voltage gauge relates to the battery SOC? I've been trying to figure out what's going on for months now. For at least the last 6 months, I've been at 15.2 -15.4 at startup, and may drop to 14.8 or so as I drive (I'm mostly doing short trips of less than 5 miles). I do put it on a charger every so often, especially if I haven't driven for a few days. The weird thing is that I haven't had any issues and ASS stills works (mostly after having it on the charger, most other times it says that it is off due to battery charging). My battery is less than 2 years old, so as long as everything is working ok I've stopped stressing about what the gauge says. Or should I be concerned that the battery is on its way out?

 

[Brian_B]

Do you know how or if the voltage gauge relates to the battery SOC? I've been trying to figure out what's going on for months now. For at least the last 6 months, I've been at 15.2 -15.4 at startup, and may drop to 14.8 or so as I drive (I'm mostly doing short trips of less than 5 miles). I do put it on a charger every so often, especially if I haven't driven for a few days. The weird thing is that I haven't had any issues and ASS stills works (mostly after having it on the charger, most other times it says that it is off due to battery charging). My battery is less than 2 years old, so as long as everything is working ok I've stopped stressing about what the gauge says. Or should I be concerned that the battery is on its way out?

So, voltage is a tricky one to look at just by itself, especially when the vehicle is running.

State of Charge is a function of voltage, current draw (in or out, that matters too), and temperature. Voltage is only one part of that equation.

If you have an open circuit battery at room temperature, then you can use a voltage chart to check the state of charge. At 12.50 volts, an AGM battery is at 80% charge (that's what the Bronco default target is). But it has to be totally open circuit - no load, and at room temp for that to be true.

When the Bronco is running, the BMS controls alternator output and that affects system voltage. What you are seeing is the BMS driving the alternator and pushing voltage up, which carries all the load on the vehicle and allows the battery to recharge -- the higher the volts, the more charge goes into the battery. So all you can really tell by your voltage reads are -- yeah, the BMS is trying to charge the battery, and those are normal voltages. High 14/low 15 volts are right in line with BMS doing a normal charge on the battery, and you can expect that almost every time you cold start the Bronco for at least some time.

The BMS will kick down to around mid-13 volts to "float" the battery and just kinda let it ride with the alternator carrying pretty much all the load - this by default occurs when the BMS thinks the battery is at 80% State of Charge by it's calculation, and will occasionally idle the alternator and you can see voltage drop in the high 12's -- that's all driven around helping fuel economy and battery longevity. You can even see some events, like rolling downhill with no accelerator input, the BMS will throw charge into the battery to help engine braking and sorta-kinda do a poor man's version of regenerative braking.

So perfectly normal to see the voltages you are seeing, especially during cold weather. Anything from low 12V (Ignition On Engine Off) to low 15V (engine on, battery charging) is perfectly normal.

 

[Bearcat1]

Try a BMS reset. The data in the BMS gets corrupted after some time. I see if all the time when I check VINs for OTA failures.

I have the same issue with the powerpoints, searched a while but couldn't find the BMS reset procedure to try? Is FDRS needed or is there another way?

 

[Brian_B]

I have the same issue with the powerpoints, searched a while but couldn't find the BMS reset procedure to try? Is FDRS needed or is there another way?

Third one down
https://www.bronco6g.com/forum/threads/bronco-cheat-codes-list.91121/

 

[rugedraw]

I have the same issue with the powerpoints, searched a while but couldn't find the BMS reset procedure to try? Is FDRS needed or is there another way?

Nah, it's super easy. Ignition on/Engine off. Flash high beams 5 times and tap the brake three times. If done correctly, you will see the battery icon flash in the IPC a few times.

Edit: It is very important to ONLY perform a BMS reset if you are 100% confident that the 12v battery is fully charged to 100%. Otherwise, you will corrupt the BMS data quality.

 

[Greg2060]

So, voltage is a tricky one to look at just by itself, especially when the vehicle is running.

State of Charge is a function of voltage, current draw (in or out, that matters too), and temperature. Voltage is only one part of that equation.

If you have an open circuit battery at room temperature, then you can use a voltage chart to check the state of charge. At 12.50 volts, an AGM battery is at 80% charge (that's what the Bronco default target is). But it has to be totally open circuit - no load, and at room temp for that to be true.

When the Bronco is running, the BMS controls alternator output and that affects system voltage. What you are seeing is the BMS driving the alternator and pushing voltage up, which carries all the load on the vehicle and allows the battery to recharge -- the higher the volts, the more charge goes into the battery. So all you can really tell by your voltage reads are -- yeah, the BMS is trying to charge the battery, and those are normal voltages. High 14/low 15 volts are right in line with BMS doing a normal charge on the battery, and you can expect that almost every time you cold start the Bronco for at least some time.

The BMS will kick down to around mid-13 volts to "float" the battery and just kinda let it ride with the alternator carrying pretty much all the load - this by default occurs when the BMS thinks the battery is at 80% State of Charge by it's calculation, and will occasionally idle the alternator and you can see voltage drop in the high 12's -- that's all driven around helping fuel economy and battery longevity. You can even see some events, like rolling downhill with no accelerator input, the BMS will throw charge into the battery to help engine braking and sorta-kinda do a poor man's version of regenerative braking.

So perfectly normal to see the voltages you are seeing, especially during cold weather. Anything from low 12V (Ignition On Engine Off) to low 15V (engine on, battery charging) is perfectly normal.

Thanks for the detailed explanation, very helpful. When I checked the actual battery voltage using a multimeter, I was at 14.55V with the engine running which I believe is normal for a AGM battery. The voltage just after shutting the engine off was 12.56 which was about right as well. The problem with trying to check the voltage with the engine off is that it continues to drop almost immediately since there is a battery draw going on as the systems are shutting down.

 

[Brian_B]

The problem with trying to check the voltage with the engine off is that it continues to drop almost immediately since there is a battery draw going on as the systems are shutting down.

Yup. Have to disconnect it (or have it under a known, controlled load like a battery tester does) to really be able to tell much

 

[HoosierDaddy]

I understand sometimes you can reactivate the battery by doing a desulfate charge. I have never tried it though so I can't verify.

My 2021 was starting to sound like it was turning over just a bit slower than normal.
I just ordered a BatteryMinder a few weeks back and let it go to work for the weekend.
It came out of desulfate mode by Sunday and was just maintaining .
All seems well at this point.

It sounds like the poor charging dynamics and A/S/S are battery killers.
It is pretty harmful to let batteries set at a state of partial charge , and that is exactly what new vehicles are doing now.

We'll see how occasional hits on the BatteryMinder work for extending battery life.

 

[Fasteddy]

Yup. Have to disconnect it (or have it under a known, controlled load like a battery tester does) to really be able to tell much

Another method of determining battery life is by measuring internal resistance, requires a specialized meter which are becoming more available at lower cost. We track internal resistance of over 400 batteries at my work as part of preventive maintenance of critical systems.

 

[feralc]

I want to add to this thread, I recently (December 2025) replaced my battery, since December 2024 I started getting the “remote features disabled to preserve battery” and as soon I turn off the engine the infotainment showed “system off to save battery”
Last December I was still under the original warranty which expired at the end of 2024, the dealer tested the battery and (of course) they said it was just fine and refused to replaced it.
Fast forward one year and the other day my truck struggled to start after 2 weeks of not being used so I started checking threads about State of Charge, Forscan, etc.
So I dusted my Forscan OBD2 cable, downloaded the latest Forscan app and dived into it.
My car showed 50% State of Charge after recharging the battery (first time I recharged it directly into the battery posts and I had a symphony of relays, then I did it on the other side of the BMS), Forscan age of the battery showed around 375 days, so the dealer did reset the BMS last year when they were testing the battery, that obviously defaulted the target to 80%, but I had battery issues constantly during the year, I didnt worry too much because I rarely use the remote features. and I never stay in the car listening to music after turning off the engine.
I tested the battery at Oreillys and they said it is fine, but not fine enough to keep up with all the Bronco systems working properly.
So I decided to buy a new battery and installed it myself, and I reset the battery age again.
Now everything works as intended, everything included that stupid ASS system I completely forgot I had because it never got engaged due to the constant lower SOC, now I have to press the button to disable it or get an eliminator, because disabling it through Forscan disables the BMS too.
What I am trying to add to this thread is that the dealer did reset my BMS without replacing the battery, I do not know if that actually helped me get an extra year of use before it actually almost left me stranded, but if the battery is not holding as it is supposed to the SOC will drop to around 50% even though the BMS thinks the battery is just one year old.

 

[B22-2023]

I tested the battery at Oreillys and they said it is fine, but not fine enough to keep up with all the Bronco systems working properly.

I had a bad cell or something and could not trickle, bench or highway charge the battery, they could see via remote my SOC was staying low. I pushed the dealer to test it and they swapped it out 60 days before warranty end.

 

[crenca]

What I am trying to add to this thread is that the dealer did reset my BMS without replacing the battery, I do not know if that actually helped me get an extra year of use before it actually almost left me stranded, but if the battery is not holding as it is supposed to the SOC will drop to around 50% even though the BMS thinks the battery is just one year old.

Curious. I wonder if they did this intentionally or was it accidental consequence of other trouble shooting/testing efforts? I suspect the latter.

Just off the top of my head, I can't think of a reason why a reset forcing the BMS to treat a battery at the end of it's life (and thus not holding volts/amps like a new one) would be helpful in extending the functionality of an end-of-life battery (on the contrary). In other words, the BMS is supposed to treat an end of life battery in such a way to help it "keep up" with the Bronco's demands...

 

[feralc]

Curious. I wonder if they did this intentionally or was it accidental consequence of other trouble shooting/testing efforts? I suspect the latter.

Just off the top of my head, I can't think of a reason why a reset forcing the BMS to treat a battery at the end of it's life (and thus not holding volts/amps like a new one) would be helpful in extending the functionality of an end-of-life battery (on the contrary). In other words, the BMS is supposed to treat an end of life battery in such a way to help it "keep up" with the Bronco's demands...

True, my understanding is that BMS sends lower voltage and amperage to new batteries to not stress them out and more voltage and amperage to older batteries to keep up, but it also resets the target to 80% thinking it is new and that might gets you more voltage/amperage in the process.
Who knows

 

[feralc]

I had a bad cell or something and could not trickle, bench or highway charge the battery, they could see via remote my SOC was staying low. I pushed the dealer to test it and they swapped it out 60 days before warranty end.

Who could see via remote your SOC was low?? The dealer can see that??

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