I have had my Xperia Ion for over a year now with zero issues. However, this week it has been shutting down for no reason at all and the intervals are getting shorter and shorter to the point where it is almost impossible to use it for anything. Along with this, the battery will jump to 1% from 85% in no time at all. It seems like the battery needs to be replaced, but what strikes me as odd is the fact that the phone only behaves this way with the sim card inserted. When the sim card is removed it typically does not act like this.
Does this sound like a battery or a simcard issue?