My driving and land conditions are such, that even with the Start-Stop feature disabled, I usually return home with the battery less than fully charged, thanks to the algorithm that tries to avoid consuming extra fuel for charging when the latter isn't strictly necessary and my drive home is mostly uphill.

 

As I make a point of not letting the battery rest at less than 12.4 V, in order to prevent sulfation, I often find myself charging the battery with my external charger between the infrequent trips.

 

I'm wondering. If I replace the original 58Ah EFB with a, say, 70Ah EFB/AGM without updating the battery specs in the car's database, will the battery voltage take longer to drop to 12,4V after a typical trip?

Could the wrong battery specs in the database have any other ill effect besides the Start-Stop not activating exactly as designed to?

 

As you know the battery only tends to charge on the overrun ( regenerative) and the battery is normally kept at around 80% charged to allow capacity for the alternator to dump charge when required on the overrun.

The chart attached shows that 12.4 V is perfectly acceptable. I believe if you fitted a different battery without coding the change in capacity then the system would not take any advantage and continue thinking capacity was same as original battery.

Edited 3 December, 20232 yr by Kenny R

8 hours ago, Kenny R said:

I believe if you fitted a different battery without coding the change in capacity then the system would not take any advantage and continue thinking capacity was same as original battery.

 

That's exactly what I think might help me. I don't want the system to restrict charging even more on account of the higher capacity of the new battery.

 

My problem is not the SOC in terms of amount of available energy. The battery has never let me down upon starting the engine. My issue is the resting voltage dropping early to 12.4 V, which induces sulfation. That's what I strive to prevent.

Thanks for the table Kenny, I saved it. Interesting the transition at 80% > 70% SOC.

You spoke of disabling the start/stop mechanism so I am assuming you would be happy to live without it of your battery would charge properly, ie in the way that they always did before all this nonsense, is that correct?

 

If so then simply disconnect the shunt resistor connector that is on the battery +ve (or is it negative?) lead and the vehicle will revert to a standard alternator charging profile, no start/stop and you can put away your battery charger for another decade!!!

 

At present you are charging it and the battery (mis)management system promptly does its best to drain that charge to allow regenerative charging nonsense, you are fighting a battle that is already lost, best bet is to hobble the system in my view, a lot less complicated compared to what you are proposing and free!

I feel that the system maintaining the battery at 80% is a bit low but it is also important that  a sealed AGM battery is not overcharged.

 

 

They cannot be topped up like old lead acid batteries were in the past. So if they are overcharged they will fail prematurely.

 

The 80% is the target because that is the minimum for the stop/start to work.

 

Maybe giving the BMS two parameters to deal with would be too complicated?

The physics is way over my head but I'm just wondering if you're over complicating the situation and thought it thru logically?

 

On 02/12/2023 at 22:12, agedbriar said:

As I make a point of not letting the battery rest at less than 12.4 V, in order to prevent sulfation, I often find myself charging the battery with my external charger between the infrequent trips.

 

I'm wondering. If I replace the original 58Ah EFB with a, say, 70Ah EFB/AGM...

 

In laymans terms, are you saying that you want to prevent premature battery failure by replacing the battery prematurely?

 

Apologies if I have that wrong.

 

EFB batteries represents the next step in technology for flooded batteries. They have longer cycle life and can cope much better with deep discharge than traditional flooded batteries.

 

 

 

https://carbatterygeek.co.uk/efb-vs-agm-battery-best-for-stop-start/

3 hours ago, kodiaqsportline said:

In laymans terms, are you saying that you want to prevent premature battery failure by replacing the battery prematurely?

 

Although it may seem so, I do not. 🙂

 

I'm wondering if, by replacing the battery (when the current one is depleted) with a bigger one without telling the system that there is now a bigger one installed, I might avoid battery sulfation without external charging between trips.

 

3 hours ago, Stonekeeper said:

EFB batteries represents the next step in technology for flooded batteries. They have longer cycle life and can cope much better with deep discharge than traditional flooded batteries.

 

 

 

https://carbatterygeek.co.uk/efb-vs-agm-battery-best-for-stop-start/

 

The damages caused by deep discharge and resting the battery below 12.4 V are different.

Repeated deep discharges cause plate distorsion which with time lead to an internal short-circuit and the unexpected battery breakdown, most likely on the road. This isn't my current topic.

 

Letting the battery rest below 12.4 V leads to sulfation, which gradually reduces the active metallic lead available for energy storage (i.e. battery capacity) and reduces the battery charging speed. The battery capacity loss is felt upon starting the engine, preventing on the road mishaps.

EFB batteries are no more sulfation resistant than conventional ones (or maybe just "somewhat", to cite the Varta representative).

1 hour ago, agedbriar said:

 

Although it may seem so, I do not. 🙂

 

I'm wondering if, by replacing the battery (when the current one is depleted) with a bigger one without telling the system that there is now a bigger one installed, I might avoid battery sulfation without external charging between trips.

 

If you replaced your existing battery with one with larger capacity - and did not adapt that new capacity into the BCM, I think you will make the present low SOC even worse, as the system will still be charging on the assumption that the smaller battery is fitted.

Edited 4 December, 20232 yr by Warrior193
repetition

5 hours ago, Warrior193 said:

If you replaced your existing battery with one with larger capacity - and did not adapt that new capacity into the BCM, I think you will make the present low SOC even worse, as the system will still be charging on the assumption that the smaller battery is fitted.

 

Well, yes, this is the line I have been thinking along.

But, what comprises the level above which the system will charge the battery only if it can do it in the so called regenerative mode? Is it a definite % of SOC or a given amount of energy stored?

 

If it's the % of SOC, a bigger battery of the same technology will start the resting period from the same voltage as the current one, but will drop to the critical 12.4 V later, which is my goal. (If this was the case, though, the system would only require the technology input, wouldn't care about nominal capacity.)

 

If it's the given amount of energy stored, a bigger battery of the same technology will stop being charged at a lower SOC, the battery will start the resting period from a lower voltage than the current one, which might even shorten the time to 12.4 V. In this case it would be better if the system didn't know that there is a bigger battery installed.

 

 

Edited 4 December, 20232 yr by agedbriar

Does the 2019 Karoq have a hybrid system?

 

Seems to me that the OP's car is working as designed, but they want to alter it for reasons that Skoda don't seem to think is an issue. And Skoda would be guided by the batteries manufacturer, though how independent the batteries manufacturer is given the conflicting thoughts on selling as many batteries as possible vs getting a reputation for having a low life and being unreliable.

 

Personally, I don't see the at rest voltage being much changed by adding extra capacity, unless it's doubled.

2 hours ago, JohnArm said:

Personally, I don't see the at rest voltage being much changed by adding extra capacity, unless it's doubled.

 

That's expected, but did you find any decrease in the at rest voltage dropping rate?

Also, do you have KESSY, which seems to be to main load at rest?

 

Edited 5 December, 20232 yr by agedbriar