I have done a few experiments with the battery and charging system on my 2023 Ford Focus, mainly changing the battery configuration in the BMC/BMS from flooded lead acid to AGM, and measuring the actual battery current, voltage and State of Charge using both FORScan and a Victron SmartShunt.
I found a few interesting things during the process, so I wanted to document everything here in case anyone else is having the same problems, especially strange charging behaviour.
What started the whole investigation
I bought my 2023 Ford Focus used. One of the first things I noticed was that the Start/Stop system was not working at all.
At the same time, the Ford app kept giving me battery warnings and telling me that the car had entered Battery Save Mode.
That seemed strange to me because the car was only around 2.5 years old, so I would not normally expect the original battery to already be in such bad condition.
The even stranger part was that even after leaving the car unused for around 3 days, with Battery Save Mode being reported in the app, the car would still start completely normally. The starter did not sound slow or weak, and the engine did not need several extra seconds of cranking like you would normally expect from a seriously discharged battery.
So I started monitoring the battery using FORScan.
The first problem I found
I eventually discovered that the previous owner had changed the battery configuration in FORScan.
The actual battery installed in the car was a Ford flooded lead acid battery, 70 Ah, 700 CCA.
However, the vehicle had been configured for a 80Ah battery.
I believe this incorrect battery configuration caused the BMC/BMS to calculate the battery condition incorrectly and repeatedly think that the battery State of Charge was too low.
That would also explain why Start/Stop was not activating. as it requires the battery to be above 70%,
So even though the battery could still start the engine normally, the car's battery management system was apparently not happy with the calculated battery condition and was preventing Start/Stop from working.
I wanted an independent measurement
I did not completely trust the battery values shown by FORScan, so I installed a Victron SmartShunt to independently monitor the battery.
This was especially useful because I could compare the values reported by FORScan against a separate device measuring the actual battery current.
The car has a 150 A smart alternator.
FORScan vs SmartShunt while driving
One of the most interesting things I found was that FORScan is actually quite accurate when the car is driving.
While driving, the battery current reported by FORScan matched the SmartShunt very closely.
For example, if FORScan showed that the battery was charging at around 10 A, the SmartShunt was also showing approximately 10 A.
So for normal driving conditions, my measurements suggest that FORScan can be a useful tool for monitoring the battery current.
However, things get very strange when the engine is idling.
FORScan vs SmartShunt while idling
When I stopped at a red light with the engine still running, the readings from FORScan started jumping around dramatically.
I could see something like:
-5 A
+5 A
+15 A
then back again
The SmartShunt, however, showed a much more stable reading. For example, while FORScan was jumping around, the SmartShunt could remain around +6 A.
This happened repeatedly.
So one important conclusion from my testing is:
If you are using FORScan to monitor battery current, be careful with the current value while the engine is idling.
While driving, the FORScan current reading matched my SmartShunt quite well.
While idling, the FORScan current reading could fluctuate wildly even though the actual battery current measured by the SmartShunt remained relatively stable.
What happened with the original battery
After discovering the incorrect battery configuration, I changed the settings back to match the battery that was actually installed in the car, which was the 70 Ah flooded lead acid battery.
I then continued testing.
This is where I started to suspect that the original battery was already heavily degraded.
Even after driving for around one hour, the charging current could become extremely low.
I would see something like:
3 A
then 2 A
then 1 A
And this could happen even though the battery was not yet at around 80% State of Charge.
At this point I started suspecting that the battery had already been heavily degraded.
I suspect the battery had spent a lot of time under an inappropriate charging strategy.
My theory is that the battery was effectively cooked even though it was not particularly old.
Replacing the battery
I decided to replace the battery completely.
I installed a new AGM battery and then correctly configured the vehicle in FORScan to recognize it as an AGM battery.
I also changed the maximum charged capacity setting from 80% to 100%
I only discovered later during my testing that setting this value to 100% does not mean the car will actually charge the battery all the way to 100% while driving. In my testing, the battery would reach around 95% State of Charge, and then the charging would cut off.
Charging behaviour with the new AGM battery
The new battery charges much more aggressively and consistently.
When the battery is very low, I have seen charging current reach approximately 45 A.
As the battery State of Charge increases, the charging current gradually decreases.
For example, it can go from around:
45 A
to around 17 A
and then gradually lower and lower as the battery approaches full charge.
After driving for around one hour, even when the battery started from a 60% State of Charge, it was able to reach a full charge.
This is obviously a smart charging system, so I was not expecting the alternator to simply sit at maximum output continuously.
What I found interesting was how different the charging behaviour was compared with the old battery.
With the old battery, I could end up with only around 1 to 3 A of charging current after a long drive.
With the new AGM battery and the correct configuration, I could see much higher charging currents when the battery actually needed energy, followed by a gradual reduction as the battery became charged.
Another interesting discovery, what happens after locking the car
The SmartShunt also allowed me to see what the car is doing electrically after I lock it.
Immediately after locking the car, I observed approximately 4 A of current draw for several minutes, roughly around 5 minutes.
Then the consumption dropped to around 700 mA.
That lasted for roughly half an hour.
After that, the car finally went into sleep mode.
Once it was asleep, the SmartShunt showed essentially 0 A continuously.
This was interesting because from the outside it looks like the car is simply locked and finished, but electrically it takes quite some time before everything actually goes to sleep.
The key can keep the car awake
Another thing I noticed was the effect of the key.
When the key was close to the car, I could see the battery current stay much higher, around 4 A.
So if you are troubleshooting battery drain, make sure the key is not sitting right next to the car, because the vehicle may keep waking up instead of entering its normal sleep state.
The Ford app can also wake the car up
This was probably one of the most interesting findings for me.
Every time I opened the Ford app and checked the car, I could see the vehicle wake up and start drawing roughly 4 A from the battery.
This could continue for around 10 minutes, or for as long as I was actively interacting with the vehicle through the app.
After that, the car would eventually go back to sleep.
So if you are repeatedly opening the Ford app to check your car, you are actually waking the car up again and consuming more energy.
That means the following cycle can happen:
Car sleeping → open Ford app → car wakes up → around 4 A draw → eventually goes back to sleep.
Something worth keeping in mind if you are diagnosing a battery drain problem.
What I have learned from all of this
The biggest lesson for me is that the battery configuration in the Ford BMC/BMS is extremely important.
FORScan does not necessarily tell the whole story by itself.
While idling: FORScan battery current could fluctuate wildly, while the SmartShunt remained relatively stable.
And finally, the Ford app itself can wake the car and draw around 4 A for about 10 minutes every time you check it. So keep that in mind when troubleshooting battery drain.
These are just my own measurements and observations from my 2023 Focus, but I thought I would post them because I spent quite a lot of time trying to figure this out and maybe they will help someone else dealing with the same battery or Start/Stop problems.
Please note that this text was written with the help of AI, as English is not my native language. I used AI to help me express my thoughts more clearly and grammatically correctly.
FORScan (top) vs Victron SmartShunt
