From our small M3W community there have been at least ten Exide 12-31 failures that we know of. It is not a case of them getting old and slowly expiring but a quick and total failure and this failure mode has been only with these batteries. There were quite a few in use as the specification for them is pretty much ideal for the M3W, unfortunately the reliability isn't.
No feedback from Exide, most people are just pleased to get going again after being stranded at the side of the road to bother taking the dead battery back to Exide. If you have one of these batteries fitted I would say it would be wise to replace it sooner rather than later, unless you enjoy lengthy, unplanned stops and calling breakdown services.
