Help.

[Ricksc]

I charge my battery out of truck because I only have street parking. Charge it all day to hit 95% SOC. Yes I know not 100 but had to put back in truck. When I put it truck it drops to 65% and I get low voltage warning. Even after resetting BMS it says low voltage. Any ideas? I upgraded 2 years ago to H7. Had no issues until 3 weeks ago with OTA update. Checked vin nothing shows needing update. Same battery monitor used while charging and while in truck.

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[PaulGrun]

Sounds like a dead battery. Yes, sometimes it’s as simple as that. Occam’s razor says that the simplest explanation is often the correct explanation.

How did you measure SOC when it was supposedly at 95%? At 66%? Remember, unless you are in an expensive laboratory and can actually measure the charge on each cell, SOC is derived based on the battery’s resting voltage.

Batteries are sort of mysterious electro-chemical beasts that often defy what us laymen think of as “common sense”.

 

[Ricksc]

With the battery monitor. Resting voltage not the problem. It’s the SOC that’s messing with truck.lowest resting voltage after 2 hours was 12.45

 

[dk2]

I've seen a few batteries have a good resting charge but then when a small load would drag them down by a cell voltage or more. They are mysterious.

 

[Ricksc]

The problem is when you take it in they test and say it’s fine. But truck tells you other wise. By turning off things to save battery. Not voltage related it’s SOC being read by the ford BMS.

 

[PaulGrun]

With the battery monitor. Resting voltage not the problem. It’s the SOC that’s messing with truck.lowest resting voltage after 2 hours was 12.45

See that was my point. You cannot actually measure SOC. It is derived from the resting voltage.
The industry (or a given manufacturer) creates a series of look up tables relating voltage to SOC. The problem is that those curves are relatively flat, so very very small differences in voltage equate to fairly large changes in “SOC”

 

[PB2021]

Do you have a model with a second battery under the rear seat? If you do as soon as you put this battery in it’s going to be charging the under seat battery impacting its own charge state

 

[Ricksc]

No I don’t. Auto store says battery test fine. Truck disagrees. 3 years and may just have to bite the bullet and buy a battery. That will make 3 batteries in 3 years.

 

[PB2021]

I would be getting the dealer to do a test for hidden draw. Should not be going through a battery a year

 

[Ricksc]

4 miles one way to work. Truck does not like short drives. Fords BMS needs some redesign. Good thing battery is 3 year free replacement.

 

[HDT05]

I'm not sure I agree that 12.56V is a 65% SOC..... I'd say that would be more in line with up around 90% - ish... which would agree with the testing...

 

[Ricksc]

I would say so too but truck keeps giving low voltage SOC and turning off things to save battery. It’s all about fords BMS system. Going to use computer to reset BMS vs the high beam and brakes method. Talked to my buddy a ford Tech he asked how I was resetting BMS. He’s never heard of that right wrong indifferent will try forscan next time. Here is today after full charge yesterday. Voltage is good but truck says low voltage SOC

 

[HDT05]

Do you have auto start stop disabled on such a short trip?

 

[PaulGrun]

Keep in mind that the purpose of a BMS reset is to notify the BMS that a new battery has been installed.
The BMS uses the age of the battery as one of many inputs to the algorithm that it uses to ‘calibrate’ SOC.
Remember, the BMS re-calibrates its idea of what the SOC is AFTER a period of rest (typically over night) by reading the current “resting” voltage.
Between re-calibration events, the BMS estimates the current SOC based on the baseline it got at the last re-calibration event and an estimate of the charge flowing into/out of the battery during normal operation.

 

[Ricksc]

Auto start stop was deleted on my truck from factory.

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