Hi Caoimhe,

From your description of the problem it sounds like something on the way out in the charging circuit. Could be wiring, the alternator or even the battery itself. It really needs to be checked by a good mechanic or auto electrician. I'd advise ringing the garage you have the warranty with and getting their go-ahead to have the car checked closer to home at their expense. It may be a quick fix after all. Either way, get it checked sooner rather than later as it could end up stranding you at the side of the road.

Best of luck