12V Battery Recharge Threshold Improved in Latest BCM Software!

[Mach-Lee]

If you can create a policy taking into account temperature, that would be better. Not sure why you wouldn't, as cold weather effects are also important....

In reality, I think we're all willing to take higher numbers, for reliability, but the reality is we give up things - like losing electrons to firing up the main systems & potentially warming the HVB - and potentially LVB long term health. Reliability is also improved because greater "distance" between when the front 12v frunk popping terminals are active, and the normal SOC.

Anyway, seems a generally good fix, although it would have seemed to me that 45% would have been "good enough".... but certainly 0.0001% getting stuck and not being able to pop the frunk is bad, when you're that person....

It's very possible the threshold may be affected by battery temperature, rate of draw, or even minimum threshold voltage regardless of SoC. That's how I'd do it to make it smarter. In the winter the LVB should be maintained at a higher level the colder it gets. May have to do some more tests when it's warmer.

The problem is not to determine what percentage is the correct value, but to know what 1% really means. The capacity will change depending on a lot of factors, so 50% one day may mean 100Wh, the other day it might be 80Wh.

To figure this out the BMS needs to monitor charging and discharging over time and make tables depending on temperature, current draw and to calculate degradation. If the battery never is discharged it will never know what 50% means. If the car is parked in a heated garage all day it might never know how low temperature affects it since it will always be charged to 100% when it is cold.

This system is probably really made for start stop systems where it needs to calculate if it can stop the engine and still be able to start again, and might not be suitable at all to monitor battery charge level over several days.

In battery systems like UPSes and memory saying devices there is a programmed full discharged cycle every month to measure and test the full capacity. There is no such thing in a car for obvious reasons, so having this 50% discharge limit is probably to try to have this cycle even when it cannot reach 100% discharge. The lower percent it can discharge to the more it will be able to calculate the full capacity, so there is a tradeoff there which is probably why they choose to to set the limit lower in the first place

Yes, battery has to cycle a little bit to establish the capacity. But the delta V on an AGM is quite high such that a 90% to 50% discharge a couple times should provide plenty of capacity data.

And yes this is the same battery sensor system carried over from start/stop vehicles, but it does also track SoC over days. It makes a measurement every 15 minutes while the car is sleeping (voltage and SoC).

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[LRinker1]

While this is great news for the battery health of our 12v batteries, one issue still remains. In the past, some of the more demanding OTA updates required that the 12v battery be at least 85% SOC to initiate the update. I have had more than one fail because my 12v battery was below that threshold. We used to have a 12v SOC value on the Ford website dashboard, but Ford decided we didn't need that anymore, so we have since been flying bling. Some folks have purchased OBD dongles that read the 12v SOC....others, like me have purchased trickle chargers to top off the 12v. Bottom line, if Ford is till pushing out updates that require that 85% threshold to succeed, this update won't address that.

I’m pleased to report that the threshold for automatic 12V recharge has been increased to 55% in the latest BCM software! This is a much-awaited improvement that will ensure the battery remains charged, healthy, and prevents it from running low or freezing in extremely cold conditions.

The original software had a threshold as low as 35%, while later versions gradually increased it to 40%, 45%, and now 55%, which is the ideal threshold.

If you’re unaware, the Mach-E automatically recharges the 12V battery when it reaches a low percentage to prevent it from dying. However, the percentage at which this automatic recharge occurs has changed in subsequent software updates.

No idea if or when it's coming OTA.