Has anyone had an issue with their SMAX (2nd gen SMAX) battery not charging, resulting in loss of stop start and heated front windscreen. Car had to have a new battery a year ago, just at the warranty period, but same issue 1 year on is happening again. Was told it is because we have not done long enough journeys to charge it for the stop start, however we have done journeys of several hundred miles at a time so said, that cannot be the reason. Anyone else had this issue? 

This is a problem with all modern Fords unfortunately.  

The only solution is to use a mains powered battery charger to top it up every few months.  Long journeys only seem to work for people doing them several times a week.

Puzzled when you say battery "not charging"?

Is this not a case of upping the charge % which may get the Stop/Start etc back (if you want it?)

Check this thread. 

My advice, change this sensor after checking the SOC by some other means. It took my 6 years to figure this out, after changing it, my SOC stays fairly constant and all my functions are working again. 

£125, change it yourself or ask Ford to do it, it's a 15min job for a good mechanic. If it's reading wonky as mine was from new, the new one works a treat. No issues since then. Hope this helps. 

Yes, it did cost me a battery at the 5 year point as that's was a hail Mary attempt to fix it. Nout wrong with the old one, but I didn't know about this sensor until afterwards. 

For ref, I have a 2017 SMax 2.0tdi 150bhp.

On 1/10/2025 at 12:46 PM, TomsFocus said:

This is a problem with all modern Fords unfortunately.  

The only solution is to use a mains powered battery charger to top it up every few months.  Long journeys only seem to work for people doing them several times a week.

It's a problem because that sensor is not well known by Ford technicians. I was lucky in that the garage I was having a free service done (I'd done something for Ford) at had a specialist tech visiting who overheard me complaining about not having a heated windscreen since month 3 of ownership.

As my car was 6 years old, he told me about the sensor and how to read it. I got the OBDLink MX reader and Car Scanner Pro app and discovered the Batt SOC was all over the place. I changed the sensor, now everything works again! Chuffed.

It fits to the rear negative battery terminal directly and measures the current and voltage in and out of the battery. Over an 8 HR period of no activity, it works out the Batt SOC and from there, the ECU knows the correct figure.

Hope this helps inform others. 🙂

I'm pleased you found a fix, but most on here know about the BMS sensor, I would really hope every Ford tech does as well.  There are some cases of incorrect sensors being fitted to some of the newer Fords, but on most of them it does just seem to be a characteristic of the charging system.

On 1/10/2025 at 12:46 PM, TomsFocus said:

This is a problem with all modern Fords unfortunately.  

The only solution is to use a mains powered battery charger to top it up every few months.  Long journeys only seem to work for people doing them several times a week.

It's a problem because that sensor is not well known by Ford technicians. I was lucky in that the garage I was having a free service done (I'd done something for Ford) at had a specialist tech visiting who overheard me complaining about not having a heated windscreen since month 3 of ownership.

As my car was 6 years old, he told me about the sensor and how to read it. I got the OBDLink MX reader and Car Scanner Pro app and discovered the Batt SOC was all over the place. I changed the sensor, now everything works again! Chuffed.

It fits to the rear negative battery terminal directly and measures the current and voltage in and out of the battery. Over an 8 HR period of no activity, it works out the Batt SOC and from there, the ECU knows the correct figure.

Hope this helps inform others. 🙂