47 minutes ago, pcaouolte said:

and reduce the gassing of polar bears).

Oh dear, all this time I was thinking it was to save the dolphins and to stop Greta having a melt down 🤣

If you want a very real solution that might actually work then you need a decent battery and a higher SOC.

If you want to watch in real time the charge conditions of the alternator and the battery then simply use FORscan on your mobile phone.

Changing the battery to the Yuasa YBX7096 EFB Start Stop Car Battery, and also changing the cars maximum 'State Of Charge' using FORScan from the factory default of 80% up to a new level of 95% might well be enough to keep fully running.

See attached two screens of my cars battery while driving at a constant speed. Note the charging current to the battery is Zero Amps. The cars SOC is set to 95% but even so the alternator will not charge the battery because the car is at a steady speed.

49 minutes ago, ASW said:

1. KwikFit AFB100 12V ECM BATTERY

2 & 3. I believe so.

"in the Winter, I use a smart battery charger to maintain a decent battery charge" I would like be able to but street parking!

 

If we're talking Kwikfit, based on comments on various sites, I would suggest they possibly didn't!

Simplified explanation: After fitting a new battery, the BMS reset lets the car know it's new. The charging system then resets to optimum for the new battery. If if isn't reset, the charging system state continues at it's sub-optimal level due to compensating over time for the reducing capacity of the old battery.

If you cannot keep your battery topped up regularly (and it appears you can't), then your battery will deteriorate quicker than normal, due to allowing it to reach high-discharge levels.

18 hours ago, pcaouolte said:

The battery is charged most when decelerating with the car in gear or going down a hill with the car in gear (it uses the alternator to add load to slow the car and charge the battery).

The battery is charged the least when accelerating or going uphill (it reduces the alternator activity to reduce load on the engine).

The battery might be charged a tiny amount when driving normally on a flat road (but it probably won't be as the alternator is switched off whenever possible to improve mpg and reduce the gassing of polar bears).

This is a simplified list. The main purpose of the smart part of the charging system is to save fuel and reduce emissions, not to keep the battery charged. 

Thanks, a helpfull clarification, I have been taking advantage of decents but not of slowing down.  Supprising that when the battery gets low there is not an automatic warning (and a switch in priority to  keep the battery operational).

18 hours ago, unofix said:

Oh dear, all this time I was thinking it was to save the dolphins and to stop Greta having a melt down 🤣

If you want a very real solution that might actually work then you need a decent battery and a higher SOC.

If you want to watch in real time the charge conditions of the alternator and the battery then simply use FORscan on your mobile phone.

Changing the battery to the Yuasa YBX7096 EFB Start Stop Car Battery, and also changing the cars maximum 'State Of Charge' using FORScan from the factory default of 80% up to a new level of 95% might well be enough to keep fully running.

See attached two screens of my cars battery while driving at a constant speed. Note the charging current to the battery is Zero Amps. The cars SOC is set to 95% but even so the alternator will not charge the battery because the car is at a steady speed.

Thanks!  

I had an initial look at the Yuasa (and have a note to look in grater detail).  As I recall it was a little deeper, can you confirm that it will fit a Mk4 Focus?

Not looked at FORScan yet, but can see the logic of raising the %.

18 hours ago, YOG said:

If we're talking Kwikfit, based on comments on various sites, I would suggest they possibly didn't!

Simplified explanation: After fitting a new battery, the BMS reset lets the car know it's new. The charging system then resets to optimum for the new battery. If if isn't reset, the charging system state continues at it's sub-optimal level due to compensating over time for the reducing capacity of the old battery.

If you cannot keep your battery topped up regularly (and it appears you can't), then your battery will deteriorate quicker than normal, due to allowing it to reach high-discharge levels.

Thanks!  I was reading "Resetting the Battery Sensor" in the mauual earlier.  Now planning to get my local garage (not electrical) to re-charge the existing battery overnight (hopefully) tomorrow and reset the BMS myself after refitted.  Have now got better guidance on "driving to charge", still lacking a simple indicator of the battery state (the light on the Auto Stop-Start button should provide some indication).

  

1 hour ago, ASW said:

can you confirm that it will fit a Mk4 Focus?

Fits all Mk4 Focus, diesel and petrol.

21 hours ago, ASW said:

Not keen on adding (yet) more electrics (!), but an in car batery voltage check would be useful. 

Voltage drain on Battery is negligible. DB1 also gives you a lot of information on the car. Yearly subscription not to bad either.

No I don't work for rewire.

10 minutes ago, jsk said:

DB1 also gives you a lot of information on the car.

Yes, very useful. All of our vehicles have them fitted.

Below is a sample of information from my Focus.

Many thanks to all who have posted responses!

Am having a Yuasa YBX7096 EFB Start Stop 75Ah 700A battery fitted today. 

Would also like to raise the State of Charge to 95% using FORScan (have a W11 laptop).  Has any task specific guidance been published (I have no ambition to change anything else)?

Just read a post saying that (in broad terms) battery charging only occurs while driving when the accellerator is not depressed (presumably while also in gear).  I assume from other posts that (effectivly) this is the case. 

9 hours ago, ASW said:

battery charging only occurs while driving when the accellerator is not depressed (presumably while also in gear).  I assume from other posts that (effectivly) this is the case. 

Effectively yes. When slowing to a stop or when going downhill in gear the smart charge system activates the alternator to add load to the engine and help slow the car down. This charges the battery. At other times you might get a slight charge but not much. 

10 hours ago, ASW said:

Am having a Yuasa YBX7096 EFB Start Stop 75Ah 700A battery fitted today. 

Ensure that the battery has been charged for at least 12 hours before fitting. New batteries are not supplied fully charged and are typically around 80% charged.

Remember to reset the BMS system was the new battery is fitted.

 

On 12/11/2025 at 11:12 AM, unofix said:

Ensure that the battery has been charged for at least 12 hours before fitting. New batteries are not supplied fully charged and are typically around 80% charged.

Remember to reset the BMS system was the new battery is fitted.

 

Thanks, on the road again! 

Working on a scheme to be able to recharge the battery in-situ when parked outside the house: Long AC extension lead + pavement cable guard then up into the ajar bonnet to a 10Amp charger (either Noco or Ctek).

Would be weather and parking dependent: trigger attempt by elapse time since last recharge (or if the Stop/Stary OFF light is no longer illuminating).

Will also seek out an Auto Electrician who can use FORScan to raise the State of Charge to 95%.

51 minutes ago, ASW said:

Will also seek out an Auto Electrician who can use FORScan to raise the State of Charge to 95%.

Have a drive up to Durham, there maybe a guy there 🤣

7 hours ago, ASW said:

Thanks, on the road again! 

Working on a scheme to be able to recharge the battery in-situ when parked outside the house: Long AC extension lead + pavement cable guard then up into the ajar bonnet to a 10Amp charger (either Noco or Ctek).

Would be weather and parking dependent: trigger attempt by elapse time since last recharge (or if the Stop/Stary OFF light is no longer illuminating).

Will also seek out an Auto Electrician who can use FORScan to raise the State of Charge to 95%.

I think you'll find it is an offence to trail a cable across pavement.

Potential for the future may be the cross-pavement charging solutions for EV's, if you were allowed to run the cable along this channel:

https://www.gov.uk/government/publications/cross-pavement-solutions-for-charging-electric-vehicles/cross-pavement-solutions-for-charging-electric-vehicles

https://energysavingtrust.org.uk/advice/cross-pavement-charging-solutions/#:~:text=Cross-pavement charging solutions allow,safely fit the charging cable.

18 hours ago, unofix said:

Have a drive up to Durham, there maybe a guy there 🤣

... it would put on some milage!

Is it something that an Auto electician could/would do (and a quick job)?

2 hours ago, ASW said:

Is it something that an Auto electician could/would do

If you find an Auto electrician who is equipped with FORScan and knows what they are doing then it should take twenty minutes.

few modern cars like more than 2 weeks between drives

10 miles once a week should be enough - so long as not stuck in town at low revs, nor with start stop rot cutting it out and killing the battery

make sure you ALWAYS turn off start stop every drive - its ONLY there to damage the car, so they can sell more cars