Hello,

Some time ago I started to notice that the Stop/Start function on my late 2018 Focus (MK4) went from working very sporadically to not working at all. The message in the Stop Start section of the info menu was "Stop Start unavailable due to vehicle recharging".

I took the vehicle to the garage to get my battery checked and was told it was at 71 percent charge (12.37V) and that the health level was 90 percent despite it being more than five years old. 

After reading similar voltages on my own with a multimeter on several different days, I decided to buy a smart charger and fully recharged the battery. The stop start function didn't work during the test drive I did after this and the same message was displayed. The most surprising thing was that after leaving the car overnight, the value I read with the multimeter was back to 12.37V, as I hadn't fully charged the battery at all! It is as if the BMS were aiming for that charge level.

Is this just a sign of an old battery that needs to be replaced, or would I be seeing other related issues if that were the case? I haven't seen any other signs of a bad battery, and recently didn't drive the car for two weeks and it was still fine.

Thank you all for your help!

 

 

Unless you start losing keyless entry, getting frequent system off to save power messages or deep sleep notifications in the Ford pass app despite using the car then the battery is probably fine. 

57 minutes ago, Alexander_ZV said:

The message in the Stop Start section of the info menu was "Stop Start unavailable due to vehicle recharging".

I took the vehicle to the garage to get my battery checked and was told it was at 71 percent charge (12.37V) and that the health level was 90 percent despite it being more than five years old

I'll try and keep this short !!

Stop/Start will not work if the SOC is 69% or less.

The Maximum factory set charge SOC is only 80%

There are approximately 112 conditions that have to be "just right" before S/S will work

Replacing a perfectly usable battery just because S/S is not working when you think it should, is not an environmentally friendly thing to do.

27 minutes ago, unofix said:

I'll try and keep this short !!

Stop/Start will not work if the SOC is 69% or less.

The Maximum factory set charge SOC is only 80%

There are approximately 112 conditions that have to be "just right" before S/S will work

Replacing a perfectly usable battery just because S/S is not working when you think it should, is not an environmentally friendly thing to do.

I knew that the battery SOC wouldn't go above around 80% through driving (to save fuel), but wouldn't an external charger be able to take it near its max charging level?

I'm just surprised that the extra charge lasted so little. Does the BMS aim for around 70-80 percent even shortly after a full charge? 

8 minutes ago, Alexander_ZV said:

I knew that the battery SOC wouldn't go above around 80% through driving (to save fuel), but wouldn't an external charger be able to take it near its max charging level?

If you use a Smart battery charger, make sure that you connect the negative lead to the vehicles chassis earth point, and not to the battery negative.

It will take at least 12 hours, possibly nearer 20 hours to get the battery to about 98%

Once you start driving the BMS will realise that the battery SOC is well above the 80% and will think "Yipee" 🎉 no need to ask the alternator to put any charge in to the battery until it falls back below 80%

The only answer is to use FORScan and change the SOC setting to 95%

27 minutes ago, unofix said:

If you use a Smart battery charger, make sure that you connect the negative lead to the vehicles chassis earth point, and not to the battery negative.

It will take at least 12 hours, possibly nearer 20 hours to get the battery to about 98%

Once you start driving the BMS will realise that the battery SOC is well above the 80% and will think "Yipee" 🎉 no need to ask the alternator to put any charge in to the battery until it falls back below 80%

The only answer is to use FORScan and change the SOC setting to 95%

Yes, I made sure I connected the negative lead to the earth point 🙂

Thanks! Your message explains what I saw after the charge.

Having ruled out a battery change, I don't think I'll bother getting this diagnosed by someone if there are 112 other parameters involved. There might not be a problem after all and if there is I haven't seen any other symptoms.

3 minutes ago, Alexander_ZV said:

if there are 112 other parameters involved. There might not be a "problem" after all and if there is I haven't seen any other symptoms.

Here you go, have a watch of this diagnostic video on Stop/Start

 

One thing I struggle to understand why the earth lead chassis point would affect the battery monitor sensor. I do use this as any sparking is away from the battery and therefore safer.

it seams to be a solid lead with the bms mounted on it . Logic would imply it wouldn’t matter providing the lead is still connected to the battery.(not charging the battery disconnected from the vehicle)

The BMS is a current sensor mounted in 'series' with the battery negative cable. It measures all current passing through the negative cable.

Connecting a battery charger negative lead directly to the battery terminal will by-pass the BMS sensor and it will not measure the charge that is being put in to the battery.

Connecting the charger negative lead to the chassis earth point or in fact any good solid earth point with a low resistance, will ensure that the BMS measures the current flow in to the battery.

In principle it wouldn't matter if you connected the charger to the battery end of the cable rather than to the battery post clamp.

In practice it's far more convenient to use the earth point, usually on the suspension tower.

Thanks, must read it inductively otherwise it would fry. My son’s Focus ( I know it’s a different charging regime and non efb battery ) just had it’s 2nd replacement ,1st done at 9.5 years, 2nd now at 16 years.