I am one of those apparently rare Volvo owners who LIKES the automatic stop/start feature, and who does not fear that it impugns my masculinity or hero-driverhood. Though it rarely worked, when it did the feature, at least in our car, operated seamlessly, and as far as I could tell had no negative features. After all, why should I sit for anywhere from 30 seconds to two minutes at a stoplight burning gas? That's just stupid. (I understand that there are those who feel stopping and starting the engine frequently can have an adverse effect on the machinery, but I'm trusting that Volvo knows what it is doing. If in the next few years we start seeing evidence that this isn't the case, I'll change my mind.)
But it rarely worked.
I have now fixed that by installing a Ctek battery charger/monitor, on the advice of several members of this forum. Stop/start now works 100 percent of the time, just as it should. The problem, apparently, was that driving the car every two or three days on relatively short trips--occasional 150-milers to/from Newark Airport--simply didn't keep the small accessory battery charged sufficiently to run the stop/start. The Ctek has totally fixed that.
Ctek is a Swedish company (though the actual units are made in China, not surprisingly), so I have to assume their chargers interface well with Volvos.