What is the logic behind the special batteries, is it just a longevity issue?
Fitting a standard wet flooded battery to a stop start systems will mean that the battery WILL FAIL, not an option of, it might fail, but it will, most likely within a couple of months of installation, 3 to 4 at the outside.
The cyclic lifespan is not good enough, and batteries like that are not designed to run with minimal charge, or even at a reduced level of charge, for long duration's, a very common scenario with stop start systems.
You must use one of the special batteries, designed to work with stop start systems.
There are a few variations on a theme, but basically you get either an EFB (Enhanced Flooded Battery), otherwise known as AFB (Advanced Flooded Battery) or ECM (Enhanced-Cycling-Mat).
EFB batteries are an enhanced version of standard wet-flooded technology. The primary benefits of EFB technology are improved charge acceptance and greater cyclic durability when operating in a reduced state of charge.
As an approximation, EFB batteries will provide 85,000 engine starts, compared to 30,000 starts from standard flooded product, in a standard vehicle (without stop start).
These tend to be fitted to lower spec vehicles in a manufacturers product line, as they are not clever as such and cannot be sued with any kind of energy recovery systems, such as regenerative braking etc.
The other most common type of battery on higher spec vehicles and more performance orientated vehicles are, Absorbent Glass Mat batteries(AGM).
AGM batteries are built using a glass mat separator which enable all the electrolyte required by the battery to be stored within the glass mat, also allowing any gasses given off during charging to be recombined into water meaning that the batteries are totally maintenance free. The design benefits of the glass mat over conventional flooded batteries enable the battery pack to operate under higher pressure without the fear of insufficient electrolyte between the plates, leading to the step change in durability offered by AGM batteries over flooded.
These batteries are almost always fitted with complicated battery management systems that link to the vehicle ECU so they can communicate and make sure that everything is working in synch. This is also why you will find these type of batteries on the higher spec cars with regenerative braking or passive boost systems. This will mean that come the time to change out an AGM battery you will also need to re link the new one with the vehicles ECU which will take the technician a bit of time and work with their diagnostic kit.
, it bothered her thinking the car had a fault, the local Ford dealer kept banging on about it needing a new battery - despite the battery being healthy enough to start first turn of the key after 3 weeks of standing - I think the stop/start ceases to function below a certain battery voltage but the battery is such heavy duty it will soldier on for a very long time of normal ie non stop/start useage...