12v battery SOC vs voltage

[MoonRiver]

Yesterday FordPass warned me of the 12v battery being low. So I ran Forscan. It shown SOC 86% but voltage 12.4. Hooked up a Deltran battery tender plus to the battery charged it all night long to full per Deltran indicator, this morning voltage went up to 14.7 but SOC didn’t charge, still 86%. Wouldn’t it be 100% since it’s fully charged?
So it looks like its voltage matters more than SOC. My question is how are these two parameters related?

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[Maquis]

Yesterday FordPass warned me of the 12v battery being low. So I ran Forscan. It shown SOC 86% but voltage 12.4. Hooked up a Deltran battery tender plus to the battery charged it all night long to full per Deltran indicator, this morning voltage went up to 14.7 but SOC didn’t charge, still 86%. Wouldn’t it be 100% since it’s fully charged?
So it looks like its voltage matters more than SOC. My question is how are these two parameters related?

If you connected directly to the battery, you bypassed the BMS so the car will have no idea you charged it.

 

[MoonRiver]

If you connected directly to the battery, you bypassed the BMS so the car will have no idea you charged it.

I connected my charger to jump start terminals under the plastic cover ( I drilled two holes to get an easy access like many others here.) Not to the battery poles. Would the BMS detect the charging current coming in?

 

[Maquis]

I connected my charger to jump start terminals under the plastic cover ( I drilled two holes to get an easy access like many others here.) Not to the battery poles. Would the BMS detect the charging current coming in?

You did it the right way.

 

[Mach-Lee]

That's normal. It's difficult to reach much higher than 90%, especially when the battery is cold. Ford's BMS has a different idea of what 100% is than your battery charger.

SoC and voltage are distinct concepts. From my FAQ:

Can I determine the SoC based on the voltage?

Not easily. Battery voltage will fluctuate based on the current draw on the battery, and whether it’s being charged. The battery could be at 70% SoC and have a voltage anywhere from 11.5V to 15.2V. This is why the car uses SoC instead of voltage to determine the 12V state. The only time SoC can be inferred from voltage is when the battery has been sitting undisturbed for at least an hour (open circuit or resting voltage) which must be measured under specific conditions (see below).

I measured the voltage with the car off and it was only 12.0V, is the battery low?

Not necessarily. First of all, you need to measure the voltage the correct way with no loads. This means letting the car go to sleep for 30 minutes before a measurement. If you just open the hood and immediately make a measurement, it will be wrong because you just woke the car up by opening the hood. You must open the hood, wait 30+ minutes, and then make a measurement without disturbing the car. Also, if your phone or fob is in your pocket and you walk up to the car, you just woke it up (so keep your phone and fob well away when taking a voltage reading). In most cases, the voltage will come back up after you let the car go to sleep. If the resting voltage after 30 mins truly is 12.0V or less, then the battery is low and should be recharged.

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