Personally I think the standard battery(like I say i'm sure it's a 250A)is little on the small side,especially when you consider a basic old style(mk3)fiesta has a 390A battery? Alot of faults with warning lights happen a crank(start up)and often combined with the clock resetting to zero,I have monitored this on examiner and noticed cluster power supply dropping as low as 7.78volts & fitted a 350A battery to cure this(it still drops to around 11volts but not enough to reset clock/date etc),this is exagerated in winter when the battery has to work harder.The alternator is up to the job to charge a 350 battery so no worries there but obviously it depends on alot of factors,short journeys,heated rear window on all the time etc.