Start-Stop system failure mode

[Crabman66]

My 77,000 mile 14 plate Elegance Greentech has recently started to sound a loud beep as  come to a full stop, when you would expect the Start Stop to activate.  The engine just continues to run and the Start-Stop icon in the dash display flashes constantly with a diagonal line across it.  
 

I am aware that this the system fail mode.  It has happened before, a couple of years ago. When this happened, the fault did not clear after a restart, and my code reader did not find any codes, but selecting ‘clear codes’ seemed to resolve the issue. Moving to the present day, when it first happened, again, there were no codes found, but clearing the codes did seem to work initially.  But now it seems to randomly happen - the car starts normally and sometimes Start-Stop will activate a couple of time perfectly fine, then all of a sudden when coming to a stop, the loud beep, flashing icon and engine continues to run.

 

I know that there are various parameters which must be met for the system to actually work, but this is a totally different issue.  There are a few other mentions on this forum of cars having done this whilst under warranty which have been cured by brake servos etc, has anyone else had any other experience of this and where to look?  
 

My thoughts are that it could be battery related. The car is on the original battery and starts well, despite over the last 13 months having gone from 15,000 miles per year to around 3,000.  I know that these cars have an AGM battery, not a conventional lead-acid one because of the stresses imposed by the Start-Stop system, and most other cars I have had have required a new battery after around 5 years. Is it possible for an AGM battery to be failing, but still provide what appears to be a good strong starting current?

 

I appreciate that I may have to resort to handing this over to the dealer to look at, but wondered if the collective knowledge on here would provide any ideas for solving this myself.

[Breezy_Pete]

I'd say it's very likely to be the battery at that age. 

[KenONeill]

On 20/05/2021 at 07:22, Crabman66 said:

My thoughts are that it could be battery related.

Could be; I've a mate who had to replace a Stop/Start battery at similar mileage.