I've own a Focus titanium x 2012 model since last November and only since the recall to fit a new coolant pipe/re route the pipe and given a  loan car had I noticed that the stop/start had not been working on my own, I thought it would kick in as it is meant to as and when it should but after having the loan car and a company car with the same feature I found that the stop/start should kick in straight away when the engine temp and car isn't requiring excess battery for the AC, So after talking with Hendy they came back saying the feature isn't that important it dosen't really save fuel and wears the starter motor down quicker as the starter was only ever meant to be used a to start the car and not constantly operate through a whole journey, I insisted that surely the feature was there for a reason and that it should save fuel and not cause any such problems as wearing the starter down or burning more fuel to start the engine over keeping it running. Dose anyone  have any info on this matter? As it stands they have charged the battery over night and it is currently working but they say after a month the battery will be lower than required to let the stop/start operate unless I do longer journey's 

Is it the original battery? If it is then it may be due a new one. Starter motor has been designed for stop start feature. 

I think the primary purpose of stop-start is to reduce pollution. It's a moot point how effective it is since pollution spikes occur during acceleration such as when taking off from traffic lights or after slowing for speed bumps. The fuel saving is probably marginal.

Hendys are correct in saying yours will stop working again if the battery is several years old. Mine is currently not working. It only worked sporadically when I first got the car 2½ years ago but did start working properly for a few days after I'd charged the battery. It doesn't work now even after a 100-mile journey and I suspect it's probably the original battery which will be 8 years old. Personally it doesn't bother me as I do virtually no urban driving so I haven't tried resetting the battery monitoring. Whilst Ian may be right that the starter motor and flywheel ring gear have been designed to cope with multiple starts it seems common sense that they'll last longer with fewer start cycles.

my battery is 5 yrs old and stop start has worked fairly consistantly in that time, mixture of urban at weekend and country roads to work in the week. max 14mile journeys. 

I'm guessing the battery hasn't been changed since new, I regular do 10 miles each way to work and 14 each way every weekend plus a fair bit further out if I'm going somewhere for something so I'd of thought it would be enough to charge it? Hendy didn't seem interested in replacing the battery at all and one of them stated he just turns his off as he is old school manically minded  

i would reset the battery monitoring and see if that gives a bit more life to your battery. 

Ign on for 10 secs

press rear foglamp switch 5 times

press hazard switch 3 times

wait up to 10 seconds while watching battery light

battery light flashes confirming completed 

ign off

Mine also works perfectly, battery is 6.5 years old, 46k miles, presumably done a lot of short journeys given that mileage, and up until recently I was doing a lot of short journeys in it, with 2 longer round trips each week.  When I bought the car the magic eye on the battery wasn't green, and the SS didn't work.  A good run followed by the battery monitor reset has seen it work perfectly for the last 6 months.   It surprises me how short a journey it will work on, literally 5 minutes from a cold morning start after being sat for days and it'll stop at traffic lights. 

There is no noticeable fuel saving, even on the manufacturers book figures it only saves 0.1mpg compared to the equivalent non-SS model.  It's purely to reduce emissions in a very localised area.  The trouble is it doesn't know how long you'll be stationary for, if it's literally 5 seconds as you shuffle forward a few yards at a time it wont be reducing emissions and that's probably the time to turn it off.  But at larger traffic light roundabouts or level crossings where you're waiting for minutes at a time, that will make a difference when most of the cars in the queue have SS.