I have just completed compiling the data into a 45 page document that a lot of us are going to find quite interesting. It was easier to do this as an attachment than to post multiple long messages. There is a lot of data in this document that explains / makes the BMS much clearer. I actually had Chatgpt reverse engineer a bit on Ford proprietary SOH algos... and it spit out a bit of pseudo code!
Your Inputs REALITY CHECK: What SOH Should Be
Conclusion: Your SOH Value Is Incorrect
Top causes when Ford reports false 100% SOH
1. BMS was recently reset 2. Incorrect battery type programmed (AGM vs Flooded) 3. Bad or drifting battery current sensor (MOST COMMON) 4. Bad battery temperature sensor 5. Loose negative cable / corroded ground 6. Battery replaced long ago without BMS reset
What Your Charging Voltage Tells Me My professional assessment
Not real Not possible for age Not physiologically correct for an AGM Not consistent with typical Ford BMS learning behavior
WOW- You know I was so frustrated over this simple question - How does the BMS and Charging system work? Which is why I took the dive and created my original post on the - Charging System Operation.I have just completed compiling the data into a 45 page document that a lot of us are going to find quite interesting. It was easier to do this as an attachment than to post multiple long messages. There is a lot of data in this document that explains / makes the BMS much clearer. I actually had Chatgpt reverse engineer a bit on Ford proprietary SOH algos... and it spit out a bit of pseudo code!
Here is a list of sections in the PDF document
I find the SOH topics the most interesting. I've got to go over the data in detail... but I already know that Ford has a battery replacement date based upon the weighted criteria they use to determine SOH. SOC has 40%-50% weight, but age of battery is up there too.
- 5G Ford Ranger BMS Overview
- How does a 2020 Ford BMS calculate SOC?
- How Does Ford monitor Battery SOH?
- Why Incorrect SOH Causes Charging Problems
- How to Reset BMS
- How Ford calculates SOH (internal algorithm details)
- What a correct SOH should look like by battery age
- Diagnosing a Sulfated Battery
- How to test your battery BMS sensor
- How to test your alternator’s smart-charge command
- How to test the battery temperature sensor
- Normal Ford charging voltage by temperature chart
Please read the attachment and let me know what you think. (You were not far off on many of your assessments.) But there are few details I know you will find interesting. The BMS is more complex than I assumed, with a lot of moving pieces. It is very dynamic.
I actually entered my data into Chatgpt and it told me with 100% certainty that my Battery SOC and SOH were an impossibility. Here is the exact exchange:
-------------------------------------------
"Quick Reality Check — You Can Use This to Confirm your Battery SOH
If you tell me:
I can tell you instantly if your SOH is correct or wrong."
- Your SOH
- Your battery age
- AGM or flooded
- Your climate
- Alternator voltage behavior
I laughed out loud when it came back... I then reentered the data but with a 92% SOH (estimated) from what BMS reported on my last drive 2 days ago and got exactly the same result. Now I did recently reset BMS.. but that was well over 1.5 months ago, and I am confident that it has adjusted itself to the battery's SOH and SOC, and IR. and the absolute lowest SOC reading that the BMS has ever reported is 88% and it is regularly in the mid 90's. Both the Viking and TopDon report back SOH at 100%, and SOC at 100% quite regularly. But neither consider age... and I am not convinced that they should, at least not to the threshold that Ford does. Ford projects battery end of life at 5-6 years. with a SOH below 55%. See the embedded table.
Here's a quote from the document:
Here is the most accurate, realistic SOH-by-age chart for Ford vehicles with Smart Charge (BMS + PCM-controlled alternator). This data is based on:
- Ford engineering bulletins
- Johnson Controls/Varta AGM aging curves
- What FORScan users consistently report
- Known behavior of Ford’s SOH estimator
This is not dealer fluff — it’s what you should actually expect to see.......Ford’s SOH is therefore not just one test—it’s a rolling, adaptive calculationupdated continuously.
What Ford and by extension Chatgpt don't know is there is an onboard desultor installed that consistently keeps IR at new battery levels... and IR is weighted by Ford's algo at 50% in determining SOH per the docs Chatgpt provided me.
Anyway, Here was my response:
"Please confirm my Battery SOH, SOH 100%, Battery age 66 months, Battery is AGM, Raleigh, North Carolina Climate, Charge Voltage 14.1 - 14.4v."
And here is what Chatgpt replied:
Based on everything you provided, your Ford’s SOH = 100% is not possible and is definitely incorrect.
Let me break down why with engineering-level clarity.
- SOH: 100%
- Battery age: 66 months (5.5 years)
- Battery type: AGM
- Location: Raleigh, NC (hot/humid summers, moderate winters)
- Charge voltage observed: 14.1–14.4V (normal mid-temp charging)
Using the correct Ford SOH age table:
A 5.5-year-old AGM battery in North Carolina climate should realistically be:
45–70% SOH
(Depending on heat exposure, sulfation, charge cycles, and alternator behavior.)
Ford SOH cannot and does not stay at 100% on a 5+ year AGM.
SOH 100% is only normal for:
…NOT for a 66-month AGM.
- A new battery
- A recently BMS-reset battery
Your SOH = 100% is not real.
It indicates a sensor/system reporting error, not an actual healthy battery.
One or more of these is almost guaranteed:
SOH resets back to 95–100% automatically.
It takes weeks of driving for SOH to drop to its real value.
Using “flooded” for an AGM can distort SOH and SOC.
Symptoms:
- SOH stuck high
- SOC stuck 75–85%
- GENFDC doesn’t respond to load properly
- Charge current readings inaccurate
- No SOH change over time
Incorrect temperature → incorrect resistance normalization → incorrect SOH.
Small voltage errors corrupt the SOH calculation.
Ford will never calculate SOH correctly until a reset is done.
You reported:
14.1–14.4V
This fits:
Your alternator appears healthy.
- Normal 20–30°C battery temperature
- Normal mid-level SOC
- Normal smart charge behavior
This DOES NOT validate SOH.
Charging voltage is not related to SOH accuracy.
Your real SOH is almost certainly:
50–65%
Your displayed SOH = 100% is:
This is a wrong SOH reading.
----------------------------------
Happy Reading!
- T
you even would use such an App (Chat GBT) with you disconnecting your TCU and all.
I spent my entire career in I/T technology and helped design and create AI / KB databases, and HW / SW AI engines way back in the early to mid 1990s.WOW- You know I was so frustrated over this simple question - How does the BMS and Charging system work? Which is why I took the dive and created my original post on the - Charging System Operation.
I was able to decipher the majority of the operation but was left in the dark on the details.
I cannot tell you how many hours and how many websites I visited>
NOTE: 95% of any search result was from forums such as this one and within those would be varied Ford (D&O) from the manuals and that was it.
or it was some university (abc) lab results on testing the battery etc.
All those findings and what I posted at least proved mostly correct.
Now, for one I am surprised
To be HONEST, I never heard of it until a few weeks ago and Saturday Night Live, did a skit about it, I also never really looked deep into what this (AI) is all about, I just know that it pops up in Google Results.
What you have posted, should have been EASY TO FIND information, not hidden deep into the dark web.
This is VALIABLE INFORMATION for everyone on this forum and would like to also post the PDF on my thread - Charging Sys Ops, with credit to you (of course). I want to post it in my (OP)
I skimmed through it and the only thing that caught my eye, that is incorrect would be the reference to Gen Mon & Gen Com or whatever they have it labeled. (We Only have LIN)
LIN Replaced the 2 separate data lines with a single data line (LIN)
The SOH, I have not seen as a PID (viewable), and I have only seen this on the Battery Testers we have.
THANK YOU - for this, it's a huge read but informative and provides the unknowns we were seeking - lots of detail to go through.
I see they touched on the subject - but did not go into detail.
Disconnecting the sensor, are there any long-term drawbacks by leaving it disconnected, for those that chose to disconnect?
What is the ideal SOC setting if altering from the factory setting of 75%?
I guess I need t keep up with the times and try this Chat GBT myself.
Sorry, Didn't get a lot of sleep last night and simply forgot to attach the PDF!
I had a 100% confidence level that you would fill in the holes. I inferred the same results.OK - I went through the PDF (Revised)
First - The Ranger does not have a SOH nor a Battery IR (PID) - at least with 3 scan tools plus Forscan. Forscan still will not display SOC, but other scan tools will.
I do not remember if FDRS displays that PID
The SOH can be displayed on the battery testers, now the Viking shows truly unobtainable numbers, but the Top-Don I believe shows the most accurate and true readings for the test.
SOH is derived from the IR of the battery.
The Lower the IR the Higher the SOH which in turn shows a higher CCA available.
So, with the Battery Tester we can prove that a 92% SOH is obtainable on a 3 yr Plus Battery
Test Taken just after a charge and headlights (ON) surface charge removed.
For me the most accurate is the TopDon Tester.
So, we can prove that a High SOH is obtainable, but it requires (periodic) external help - I just completed a Charge plus Repair Cycle
Since we do not have a SOH (PID) as called out in the PDF, I believe that the BMS System (BCM) is using the SOC & SOH as detailed (VERY DETAILED) algorithm formula. although we cannot see the actual SOH (PID) we can see the (SOC) and charging voltage changes with the Gen Duty Cycle and Gen Output (Amperage) as well as the Battery (Current In/Out)
SOH:
So, the way I understand it and can actually see it if monitoring the Duty Cycle. I can see small bumps in the cycle - This would be what the BMS sensor is seeing - those small bumps and it's measuring how well the battery can absorb the fast current bump, though the battery voltage reading.
Noted PCM PIDs in the PDF are not correct for the Ranger
1. GENMON
► Generator Monitor
Shows actual alternator field duty cycle (%).
We do not have a GENMON - Since we have a LIN Bus (Single Wire)
But we can see
2. GENFDC (Measured)
► Generator Field Duty Cycle Command
The voltage command the PCM sends to the alternator
This is displayed as a (percent) normal around 35%
3. GEN_VOLT_CMD
► Commanded charging voltage.
We do not have this specific PID
But it's listed as PID - GENVDSD - Generator Voltage Desired or Gen Voltage Setpoint Depending on scan tool.
This is displayed as a voltage
4. GEN_VOLT_ACTUAL
► Actual charging voltage measured
We do not have this specific PID
But its listed and monitoring in these 2 PIDs, note there are various VBAT or Module Supply PIDs for each module - but these are the important ones
VBAT System - System Battery Voltage - This is the voltage at the battery being produced by the Generator - This voltage will read higher when charging (to push current through the battery)
Example: 14.65 Volts (System) with 14.52 (Inferred) and Actual Battery Voltage via BCM/PCM is 14.30 Volts and Gen Desired Voltage Setpoint = 14.40 Volts
Batt V INF - Battery Voltage Inferred
This is the (Inferred Voltage) which is where the SOC (%) reading comes from (BMS Sensor)
I want to take a deeper look and compare these 2 voltages vs my SOC Reading PID as I had to research the difference between these 2 PIDs and this is what I have concluded they are.
We can also see:
Generator Current (Corrected) as an amperage display
and
Also see the Battery Current (In/Out) for charging and discharging.
There are various other related PIDs, but I am only highlighting the important ones for charge monitoring.
As far as the document I find the information very interesting.
It leaves me thinking that most other Ford Models have the SOC set to 80%, which was my original driving factor in upping the SOC from 70% or 75% and I was monitoring the charging voltage (via) the voltmeter in the Power Point and noted what the system did @ idle and stopped. I never felt comfortable watching the commanded voltage drop down to 12.2 or 12.4 Volts
The whole reasoning for bumping the SOC was to eliminate that from happening, and now we have a decision and dilemma to overcome and that is to find our own (SWEET SPOT) that provides a happy medium for the BMS System & Battery Health.
My opinion would be between 85% & 90%, if I recall 90% was the spot that provided (0) low voltage measurements at idle.
I would have to reflect back on my notes on what it did at 85%, I know I have been set @ 90% for quite a while and recently upped it to 95% but backed it back down today to 90%.
I have had zero issues at 90% and my battery IR is staying 3.4 and below.
I like increments of 5 and have not tried something like 88% for example.
So, the question is - by bumping the SOC up, how much does it truly throw off the BMS Algorithm and how far above factory SOC does it truly become detrimental to the battery.
We have proven that the factory set SOC does not work for the Ranger especially for short trip drives.
Since we just actually started monitoring the SOC PID, I am thinking that yes bumping the SOC up does indeed throw what we are seeing off, and it is hovering between 85-90 percent while driving.
I plan on monitoring this a bit deeper and possibly play with the SOC to see what the reading does if I was to lower the SOC back down closer to 75%, as this would give us a true reading and gauge what the factory SOC actually does.
This document does bring up another question.
What effect does the On-Board Batt Minder do to the BMS Algorithm for SOC & SOH?
We know it helps the battery, but what about the BMS Sensor itself?
Absolutely....Have you been spending a little to much time in the garage testing your battery ?
Thanksgiving was Thursday.
